AGC 226178 and NGVS 3543: Two Deceptive Dwarfs toward Virgo

Abstract

The two sources AGC 226178 and NGVS 3543, an extremely faint, clumpy, blue stellar system and a low surface brightness dwarf spheroidal, are adjacent systems in the direction of the Virgo cluster. Both have been studied in detail previously, with it being suggested that they are unrelated normal dwarf galaxies or that NGVS 3543 recently lost its gas through ram pressure stripping and AGC 226178 formed from this stripped gas. However, with Hubble Space Telescope Advanced Camera for Surveys imaging, we demonstrate that the stellar population of NGVS 3543 is inconsistent with being at the distance of the Virgo cluster and that it is likely a foreground object at approximately 10 Mpc, whereas the stellar population of AGC 226178 is consistent with it being a very young (10–100 Myr) object in the Virgo cluster. Through a reanalysis of the original ALFALFA H i detection, we show that AGC 226178 likely formed from gas stripped from the nearby dwarf galaxy VCC 2034, a hypothesis strengthened by the high metallicity measured with MUSE VLT observations. However, it is unclear whether ram pressure or a tidal interaction is responsible for stripping the gas. Object AGC 226178 is one of at least five similar objects now known toward Virgo. These objects are all young and unlikely to remain visible for over ∼500 Myr, suggesting that they are continually produced in the cluster.

Young, Blue, and Isolated Stellar Systems in the Virgo Cluster. II. A New Class of Stellar System

“…The object we refer to as BC3 is an independent reidentification (based on optical appearance) of the H I-selected object AGC 226178 from the ALFALFA survey (Haynes et al 2011;Cannon et al 2015). This object has already been studied in detail (Cannon et al 2015;Junais et al 2021;Jones et al 2022) and is the BC most similar to SECCO 1.…”

“…and R F814W values of Schlafly & Finkbeiner (2011) were used to correct for Galactic extinction at the position of each source. Stars were selected from the resulting DOLPHOT catalog following a similar approach to Jones et al (2022). Briefly, we select all point-like (type 1 and 2) objects with no photometry flags from the DOLPHOT source catalog.…”

“…As alluded to by Sand et al (2017) and Jones et al (2022), these two objects are not unique but instead appear to be part of a larger population of similar objects in Virgo. SECCO 1 and AGC 226178 were originally identified through their H I line emission, thereby guaranteeing gas richness.…”

“…However, attempts to distinguish these objects have led to surprising discoveries, most notably SECCO 1 (also called AGC 226067; Adams et al 2013Adams et al , 2015Bellazzini et al 2015;Sand et al 2015;Beccari et al 2017a;Sand et al 2017;Bellazzini et al 2018) and AGC 226178 (Cannon et al 2015;Junais et al 2021;Jones et al 2022). These are two young, blue, extremely low-mass (M * ∼ 10 5 M e ), gas-rich, metal-rich, actively starforming stellar systems in the Virgo cluster.…”

“…24 The properties of both systems imply that they formed via in situ star formation (SF) in gaseous debris stripped from a much larger object. In the case of AGC 226178, the likely parent object has been identified as the nearby galaxy VCC 2034, to which it is connected via a tenuous, low-columndensity, 70 kpc long H I bridge (Jones et al 2022). However, it is unclear whether this gas was stripped by a high-speed tidal encounter, or by ram pressure from the intracluster medium (ICM).…”