Hubble Space Telescope  Imaging of the Ultra-compact High Velocity Cloud AGC 226067: A Stripped Remnant in the Virgo Cluster

Abstract

We analyze the optical counterpart to the ultra-compact high velocity cloud AGC226067, utilizing imaging taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. The color-magnitude diagram of the main body of AGC226067 reveals an exclusively young stellar population, with an age of ∼7-50 Myr, and is consistent with a metallicity of [Fe/H]∼−0.3 as previous work has measured via H II region spectroscopy. Additionally, the color-magnitude diagram is consistent with a distance of D≈17 Mpc, suggesting an association with the Virgo cluster. A secondary stellar system located ∼1 6 (∼8 kpc) away in projection has a similar stellar population. The lack of an old red giant branch (5 Gyr) is contrasted with a serendipitously discovered Virgo dwarf in the ACS field of view (Dw J122147+132853), and the total diffuse light from AGC226067 is consistent with the luminosity function of the resolved ∼7-50 Myr stellar population. The main body of AGC226067 has a M V =−11.3±0.3, or M stars =5.4±1.3×104 M e given the stellar population. We searched 20 deg 2 of imaging data adjacent to AGC226067 in the Virgo Cluster, and found two similar stellar systems dominated by a blue stellar population, far from any massive galaxy counterpart-if this population has star-formation properties that are similar to those ofAGC226067, it implies ∼0.1 M e yr −1 in Virgo intracluster star formation. Given its unusual stellar population, AGC226067 is likely a stripped remnant and is plausibly the result of compressed gas from the ram pressure stripped M86 subgroup (∼350 kpc away in projection) as it falls into the Virgo Cluster.

WALLABY pre-pilot survey: Two dark clouds in the vicinity of NGC 1395

“…Figure 9 shows that both C1 and C2 are: 1) consistent with the HI size-mass relationship that is found for low-mass and low surface brightness galaxies in the Local Universe, including rotationallysupported TDGs; 2) are only a factor of a few less massive in HI than both the Small and Large Magellanic Clouds; and 3) are factors of a few more massive than the 'almost-dark' galaxies, Coma-P (Brunker et al 2019) or Secco-I (Sand et al 2017). The consistency of C1's and C2's HI properties with that of the HI size-mass relationship may be suggestive of rotational support at some level even if our current ASKAP HI observations only show support for rotation in C2.…”

Galaxy Evolution in Clusters

“…The H I masses of those clouds are 10 7.28 and 10 7.85 M -both numbers are within our clump mass distribution, but at the upper end, which could possibly mean an observational bias. Another cloud has been reported in Sand et al (2017), with a stellar mass of 5.4 ± 1.3 × 10 4 M (also within our predicted range), and a stellar age of ∼ 7 -50 Myr, relatively small compared to our clump lifetime, but consistent with it.…”

“…where isolated H I clouds without any apparent connection to a galaxy, sometimes hosting young stellar populations, have been observed (e.g. de Mello et al, 2008;Torres-Flores et al, 2009;Kent, 2010;Sand et al, 2017). Such objects have not received a comprehensive treatment in the literature so far, except within the local group, where analogous objects have been named Ultra Compact High Velocity Clouds (UCHVCs, see e.g.…”

An H$α$/X-ray orphan cloud as a signpost of the intracluster medium clumping

“…none found in the Hα surveys in the Coma cluster, A851, and CL0024+17 (Yagi et al 2010(Yagi et al , 2015. The only other isolated Hα cloud in a galaxy cluster we are aware of is SECCO 1 in the Virgo cluster (Beccari et al 2017;Sand et al 2017;Bellazzini et al 2018). SECCO 1 is a faint, star-forming stellar system with some diffuse Hα emission.…”