A very dark stellar system lost in Virgo: kinematics and metallicity of SECCO 1 with MUSE

Abstract

We present the results of VLT-MUSE integral field spectroscopy of SECCO 1, a faint, star-forming stellar system recently discovered as the stellar counterpart of an Ultra Compact High Velocity Cloud (HVC274.68+74.0), very likely residing within a substructure of the Virgo cluster of galaxies. We have obtained the radial velocity of a total of 38 individual compact sources identified as Hii regions in the main and secondary body of the system, and derived the metallicity for 18 of them. We provide the first direct demonstration that the two stellar bodies of SECCO 1 are physically associated and that their velocities match the Hi velocities. The metallicity is quite uniform over the whole system, with a dispersion lower than the uncertainty on individual metallicity estimates. The mean abundance, 12 + log(O/H) = 8.44, is much higher than the typical values for local dwarf galaxies of similar stellar mass. This strongly suggests that the SECCO 1 stars were born from a pre-enriched gas cloud, possibly stripped from a larger galaxy. Using archival HST images we derive a total stellar mass of 1.6 × 10 5 M for SECCO 1, confirming that it has a very high Hi to stellar mass ratio for a dwarf galaxy, M Hi /M * ∼ 100. The star formation rate, derived from the H α flux is a factor of more than 10 higher than in typical dwarf galaxies of similar luminosity.

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

“…The main stellar body of AGC 226067 consists primarily of blue stars in several distinct clumps. A second clump of blue stars ∼1.6 arcmin to the northwest of the main body of AGC 226067 is seen, as has been noted in previous work (Adams et al 2015;Sand et al 2015;Beccari et al 2016Beccari et al , 2017a. In contrast, an uncataloged Virgo cluster dwarf galaxy serendipitously in our ACS field of view (which we dub Dw J122147+132853) consists almost entirely of RGB stars, which we discuss below.…”

“…Several previous works have also pointed out a secondary clump of blue stars (Figure 1), located ∼1 6 (∼8 kpc) to the northeast of the main body of AGC226067 (Adams et al 2015;Sand et al 2015;Beccari et al 2016Beccari et al , 2017a. A CMD of this region is shown in the middle-left panel at the top of Figure 2.…”

“…6 M e stellar population with ages between ∼7-50 Myr and a [Fe/H]=−0.3 (corresponding to the gas-phase metallicity found by Beccari et al 2017a, assuming the solar abundance of Grevesse et al 2007) at a distance of 17 Mpc (we assumed a Kroupa initial mass function; Kroupa 2001). We have convolved the simulated data set with our measured photometric uncertainties.…”

“…Follow-up highresolution H I observations with the Very Large Array showed that AGC 226067 broke up into two distinct H I clouds (Adams et al 2015)-the primary H I source is coincident with the optical/UV counterpart, while the secondary H I component also has an optical/UV counterpart offset by 0 5. Data from the Multi Unit Spectroscopic Explorer (MUSE) at the VLT revealed 38 separate H II regions scattered throughout the main and secondary stellar body of AGC 226067, with a nearly uniform metallicity of 12 log O H 8.37 á + ñ = ( ) (for the main body), more metal-rich than expected if AGC 226067 was a gas-rich dwarf galaxy (Beccari et al 2017a). AGC 226067 is projected onto the "Low Velocity Cloud" region of the Virgo Cluster (at D≈17 Mpc, which we use throughout this work; Boselli et al 2014), which has a velocity distribution centered at v LSR ∼ 0 km s −1 with a range of ±400 km s −1 .…”

Star–Disk Interactions in Multiband Photometric Monitoring of the Classical T Tauri Star GI Tau

“…In distant clusters, properties of low-mass stars are often inferred from photometry (e.g., Reggiani et al 2011;Jose et al 2016;Beccari et al 2017). Extinction events, accretion bursts, and spots each influence the inferred mass and age of member stars.…”