Closing the gap: Follow-up observations of peculiar dusty objects close to Sgr A* using ERIS

TL;DR

Using ERIS SPIFFIER, this study extends the Galactic-center monitoring of dusty S-cluster objects by testing Keplerian orbits for G2/DSO, D9, and X7, and examining X3, thereby closing the 2019–2024 observational gap. The authors recover the targets at their predicted positions, measure Br$\gamma$ emission, and update orbital elements with only modest deviations ($<2\%$) from earlier fits, reinforcing the Keplerian framework around Sgr A$^*$. They report no significant Br$\gamma$ variability for G2/DSO, confirm the D9 binary’s ongoing periodic signal, and find X7 to follow a Keplerian trajectory, while X3 shows persistent Br$\gamma$ doublet features and evidence for outflows. The work showcases ERIS’s enhanced astrometric and spectroscopic capabilities, setting the stage for deeper insights with JWST/MIRI and ELT-era instruments to probe the Galactic-center environment at sub-percent precision.

Abstract

Context. In addition to the supermassive black hole Sgr A*, the inner parsec of our Galactic center is home to numerous fruitful scientific habitats. One of these environments is the S cluster, which consists of two distinct populations: the main-sequence S stars and the dusty G objects. While the majority of the brightest S stars can be classified as young B stars, the G sources can be described as dusty objects whose nature is still under debate. Aims. In this work, we focus on the most prominent G objects in the S cluster and follow their Keplerian trajectory around Sgr A*. With this, we test the predictions based on almost two decades of monitoring of the direct vicinity of our central supermassive black hole using NACO and SINFONI, formerly mounted at the Very Large Telescope (VLT). The goal is to increase the existing data baseline for G2/DSO, D9, and X7 to get insights into their evolution on their Keplerian trajectories. In addition, we revisit the massive Young Stellar Object (YSO) X3 and scrutinize the potential impact of its environment on this highly dynamic source. Methods. The successor to the two instruments is called ERIS and offers upgraded optics and improved properties, including an enhanced spectral resolution. We utilize the IFU mode of ERIS, called SPIFFIER. We search for the Doppler-shifted Brγ emission line to rediscover peculiar objects in the S cluster using SPIFFIER with the highest available spatial plate scale of 12.5 mas. Furthermore, we will derive the Brγ luminosity of G2/DSO to inspect the degree of its change more than ten years after the pericenter passage. If present, a decrease in the Brγ luminosity of G2/DSO on its descending part of the orbit would directly impact the direction of the debate about its nature.

Figures (18)

• Figure 1: Multiwavelength finding chart of the inner $\approx$0.8 pc of the Galactic center. For this representation of the fraction of the inner parsec, we use ALMA continuum data observed at ($9.99\pm1.58$)$\times10^{10}$ Hz, which is represented as green in the plot. The red background image and blue emission is observed with NACO in the K- and L-band, respectively. We overlay the plot with the magenta-colored Doppler-shifted Br$\gamma$ emission line observed at 2.1648 µ m using ERIS and a related width of $\pm 330$ km/s. The contour lines represent 9$\%$, 13$\%$, 26$\%$, 30$\%$, 43$\%$, and 65$\%$ of the peak emission of IRS 13 of about $\rm 0.9\times10^{-6}\,{\rm W/cm^2}$Maillard2004.
• Figure 2: Detection of G2/DSO on its Keplerian orbit with ERIS in 2024. The Br$\gamma$ line map illustrates the preserved compact shape of G2/DSO and its continued path on a Keplerian orbit. The image is centered on Sgr A* and shows continuum contour lines of the brightest S cluster stars. The location of S2, Sgr A*, and G2/DSO is indicated. North is up, east is to the left.
• Figure 3: Magnitude and luminosity evolution of G2/DSO. The continuum detection is limited to 2019, whereas we added a new Br$\gamma$ luminosity data point representing the ERIS observations in 2024. As we mentioned in peissker2021c, we find no signatures of variability for G2/DSO. Follow-up studies will focus on the continuum detection and evolution of the source.
• Figure 4: Doppler-shifted Br$\gamma$ line detection of D9 and D2 with ERIS in 2024. The white orbit plot indicates the trajectory of D9. Furthermore, the path and source are denoted with white arrows. In addition, we include the Keplerian approximation of D2 adapted from Peissker2020b. The magenta arrows show the source and trajectory of the dusty object D2 that was in superposition with D23 in 2019 Peissker2024a. We expect increased confusion for both D9 and D2 from 2025 to 2027. The dusty source D23 moved out of the FOV in 2024 and is not visible in this figure.
• Figure 5: Resulting periodic plot of the D9 binary system. The plot does cover almost 20 years of ongoing IFU efforts in the Galactic center, including SINFONI and ERIS. The black data points are based on ERIS observations and are at their expected spectroscopic position. For the gap between 2019 and 2022, no IFU observations of the Galactic center are available.