arXiv subjects

Á. Martínez-Arranz

Publications and source records attributed to Á. Martínez-Arranz.

4 recordsLinked to original sources

arXiv2026

Age and metallicity of the Milky Way's nuclear star cluster studied at 3 pc from Sagittarius A*

The Milky Way's nuclear star cluster (NSC) is a unique laboratory to study the formation and evolution of dense stellar systems around a supermassive black hole. Previous work suggests that most stars in the NSC are old; however, the detailed age and metallicity distributions remain uncertain. We constrain the star formation history (SFH) and metallicity of a poorly explored region located $\sim$3 pc from SagittariusA*. We analyse VLT/NACO imaging in an intermediate-band filter centred at 2.24 $μ$m, complemented by $H$-band data. We construct completeness-corrected $K$-band luminosity functions (LFs), clearly identifying the Red Clump and Red Giant Branch Bumps. The SFH is derived by fitting cumulative LFs with MIST, PARSEC, and BaSTI models spanning a wide range of ages and metallicities, using Monte Carlo sampling to estimate uncertainties. Metallicity constraints are refined using spectroscopic measurements from the literature. The stellar population is predominantly old and metal-rich: $75.6 \pm 9.5$% of the stellar mass formed $\gtrsim 10$ Gyr ago, with median [M/H] $\sim +0.35$. An intermediate-age component at 2-3 Gyr contributes $20.8 \pm 8.7$%, while minor populations are present at $\sim$400 Myr ($0.9 \pm 0.8$%) and 20 Myr ($3.6 \pm 1.4$%), the latter representing a small but non-negligible young population. Systematic uncertainties from stellar models, binning, photometric range, unresolved binaries, and filter choice are assessed. These results indicate early dominant formation, a significant 2-3 Gyr episode, and minor recent activity, consistent with spectroscopic measurements and with properties of the inner NSC and nuclear stellar disc.

astro-ph.GA↗

arXiv2024

Spectroscopy evidence for a so far unknown young stellar cluster at the Galactic Center

The Nuclear Stellar Disk has been a highly active star-forming region in the Milky Way for approximately the last 30 million years. Despite hosting prominent clusters like Arches, Quintuplet, and Nuclear Stellar, their combined mass is less than 10% of the expected stellar mass, leading to the "missing cluster problem." Various factors, including high stellar density and tidal forces, contribute to this absence of clusters. Traces of dissolving clusters may exist as co-moving groups of stars, shedding light on the region's star formation history. Our analysis, utilizing integral field spectroscopy and astrophotometric data, reveals a group of young stellar objects in the NSD sharing velocities and positions, potentially indicating remnants of dissolved clusters or stellar associations. This finding contributes valuable insights into the understanding of the missing clusters problem in the Galactic center.

astro-ph.GA↗

arXiv2023

Co-moving groups around massive stars in the Nuclear Stellar Disk

During the last $\sim$ 30 Myr the nuclear stellar disk in the Galactic center has been the most prolific star forming region of the Milky Way when averaged by volume. Remarkably, the combined mass of the only three clusters present today in the nuclear stellar disk adds up to only $\sim$10\% of the total expected mass of young stars formed in this period. Several causes could explain this apparent absence of clusters and stellar associations. The stellar density in the area is so high that only the most massive clusters would be detectable against the dense background of stars. The extreme tidal forces reigning in the Galactic center could dissolve even the most massive of the clusters in just a few Myr. Close encounters with one of the massive molecular clouds, that are abundant in the nuclear stellar disk, can also rapidly make any massive cluster or stellar association dissolve beyond recognition. However, traces of some dissolving young clusters/associations could still be detectable as co-moving groups. It is our aim to identify so far unknown clusters or groups of young stars in the Galactic Center. We focus our search on known, spectroscopically identified massive young stars to see whether they can pinpoint such structures. We created an algorithm to detect over-densities in the five-dimensional space spanned by proper-motion, position on the plane of the sky and line-of-sight distances, using reddening as a proxy for the latter. Since co-moving groups must be young in this environment, proper motions provide a good means to search for young stars in the Galactic center. We found four co-moving groups around massive stars, two of which are very close in position and velocity to the Arches' most likely orbit

astro-ph.GA↗

arXiv2022

Distance to the Brick cloud using stellar kinematics

Context. The central molecular zone at the Galactic center is currently being studied intensively to understand how star formation proceeds under the extreme conditions of a galactic nucleus. Knowing the position of molecular clouds along the line of sight toward the Galactic center has had important implications in our understanding of the physics of the gas and star formation in the central molecular zone.It was recently claimed that the dense molecular cloud G0.253 + 0.016 (the Brick) has a distance of $\sim$7.20 kpc from the Sun. That would place it outside of the central molecular zone, and therefore of the nuclear stellar disk, but still inside the Bulge. Aims. Theoretical considerations as well as observational studies show that stars that belong to the nuclear stellar disk have different kinematics from those that belong to the inner Bulge. Therefore, we aim to constrain the distance to the Brick by studying the proper motions of the stars in the area. Results. The stellar population seen toward the nuclear stellar disk shows the following three kinematic components: 1) Bulge stars with an isotropic velocity dispersion of $\sim$3.5 micro-arc second per year; 2) eastward moving stars on the near side of the nuclear stellar disk; and 3) westward moving stars on the far side of the nuclear stellar disk. We clearly see all three components toward the comparison field. However, toward the Brick, which blocks the light from stars behind it, we can only see kinematic components 1) and 2). Conclusions. While the Brick blocks the light from stars on the far side of the nuclear stellar disk, the detection of a significant component of eastward streaming stars implies that the Brick must be located inside the nuclear stellar disk and, therefore, that it forms part of the central molecular zone.

astro-ph.GA↗