Discovery of 18 Stars with −3.10 < [Fe/H] < −1.45 in the Sagittarius Dwarf Galaxy*

Abstract

Studies of the early chemical evolution of some larger dwarf galaxies (> 10 7 M ) are limited by the small number of stars known at low metallicities in these systems. Here we present metallicities and carbon abundances for eighteen stars with metallicities between −3.08 ≤ [Fe/H] ≤ −1.47 in the Sagittarius dwarf spheroidal galaxy, using medium-resolution spectra from the MagE spectrograph on the Magellan-Baade Telescope. This sample more than doubles the number of known very metal-poor stars ([Fe/H] ≤ −2.0) in the Sagittarius dwarf galaxy, and identifies one of the first known extremely metal-poor stars ([Fe/H] ≤ −3.0) in the system. These stars were identified as likely metal-poor members of Sagittarius using public, metallicity-sensitive photometry from SkyMapper DR1.1 and proper motion data from Gaia DR2, demonstrating that this dearth of metal-poor stars in some dwarf galaxies can be addressed with targeted searches using public data. We find that none of the stars in our sample are enhanced in carbon, in contrast to the relative prevalence of such stars in the Milky Way halo. Subsequent high-resolution spectroscopy of these stars would be key in detailing the early chemical evolution of the system.

The Pristine Inner Galaxy Survey (PIGS) IV: A photometric metallicity analysis of the Sagittarius dwarf spheroidal galaxy

“…The study of iron-depleted stars is of great interest for reconstructing the history of the Sgr galaxy, as they carry essential information to draw the story line of the early evolution of their host galaxy. Different investigations of VMP stars in Sgr over the years have led to an improved understanding of the early evolution of this dissolving system (Bellazzini et al 2008;Hansen et al 2018;Chiti & Frebel 2019;Chiti et al 2020), but these are based on just a handful of known very metal-poor stars. The blue, metal-poor region of the Sgr CMD overlaps with the giant branch of the Galactic bulge, and before the Gaia data became available it was difficult to disentangle these.…”

“…The blue, metal-poor region of the Sgr CMD overlaps with the giant branch of the Galactic bulge, and before the Gaia data became available it was difficult to disentangle these. Chiti & Frebel (2019) and Chiti et al (2020) used the Gaia data in combination with narrow-band SkyMapper 𝑣 photometry to identify 22 metal-poor stars (−3.10 < [Fe/H] < −1.45) in Sgr, which was successful but still resulted in only a small sample.…”

“…systems may have contributed to the formation of more massive ones, which could have happened to Sagittarius (Chiti et al 2020). A recent work by Malhan et al (2022) found that the metal-poor Elqui stream is associated with Sagittarius and was likely accreted inside the Sgr dSph.…”

“…Despite being one of the most massive dSph satellite galaxies around the MW, after the Large Magellanic Cloud and Small Magellanic Cloud, Sgr hosts stars with metallicities down to the extremely metal-poor regime, a metallicity range which is commonly found in smaller dwarf systems (Frebel et al 2010). To date, only ∼20 very metal-poor (VMP, [Fe/H] < −2.0) stars have been discovered and studied with either high-or low-resolution spectroscopy in Sgr (Bellazzini et al 2008;Mucciarelli et al 2017;Hansen et al 2018;Chiti & Frebel 2019;Chiti et al 2020). This very metal-poor population in Sgr still requires further investigation.…”

Beyond spectroscopy. I. Metallicities, distances, and age estimates for over twenty million stars from SMSS DR2 and Gaia EDR3

“…The special design of the uv filters provide photometric sensitivity to stellar surface gravity and metallicity (Bessell et al 2011). The ability of these two filters to extract surface-gravity and metallicity information has been well-demonstrated by several studies using SMSS DR1.1 (e.g., Casagrande et al 2019;da Costa et al 2019;Huang et al 2019;Chiti et al 2020). Compared to SMSS DR1.1, SMSS DR2 has now released photometric data for a substantially larger number of astrophysical sources, including more data from the Shallow Survey and the deeper Main Survey.…”