First resolved stellar halo kinematics of a Milky Way-mass galaxy outside the Local Group: The flat counter-rotating halo in NGC 4945

被引：0

作者：

Beltrand, Camila ^{[1
]}

Monachesi, Antonela ^{[1
]}

D'Souza, Richard ^{[2
]}

Bell, Eric F. ^{[3
]}

de Jong, Roelof S. ^{[4
]}

Gomez, Facundo A. ^{[1
]}

Bailin, Jeremy ^{[5
]}

Jang, In Sung ^{[6
]}

Smercina, Adam ^{[7
]}

机构：

[1] Univ La Serena, Dept Quim, Ave Raul Bitran 1305, La Serena, Chile

[2] Specola Vaticana, Vatican Observ, I-00120 Vatican City, Vatican

[3] Univ Michigan, Dept Astron, 311 West Hall,1085 South Univ Ave, Ann Arbor, MI 48109 USA

[4] Leibniz Inst Astrophys Potsdam AIP, Sternwarte 16, D-14482 Potsdam, Germany

[5] Univ Alabama, Dept Phys & Astron, Box 870324, Tuscaloosa, AL 35487 USA

[6] Univ Chicago, Dept Astron & Astrophys, 5640 S Ellis Ave, Chicago, IL 60637 USA

[7] Univ Washington, Dept Astron, Box 351580, Seattle, WA 98195 USA

来源：

ASTRONOMY & ASTROPHYSICS | 2024年 / 690卷

基金：

美国国家科学基金会;

关键词：

galaxies: halos; galaxies: individual: NGC 4945; galaxies: kinematics and dynamics; galaxies: stellar content; LARGE-SCALE STRUCTURE; ELEMENTAL ABUNDANCES; GLOBAL PROPERTIES; ANDROMEDA GALAXY; ACCRETION ORIGIN; SPIRAL GALAXIES; GHOSTS SURVEY; IN-SITU; METALLICITY; MERGER;

D O I：

10.1051/0004-6361/202450626

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

The stellar halos of galaxies, primarily formed through the accretion and merger of smaller objects, are an important tool for understanding the hierarchical mass assembly of galaxies. However, the inner regions of stellar halos in disk galaxies are predicted to have an in situ component that is expected to be prominent along the major axis. Kinematic information is crucial to disentangle the contribution of the in situ component from the accreted stellar halos. The low surface brightness of stellar halos makes it inaccessible with traditional integrated light spectroscopy. In this work, we used a novel technique to study the kinematics of the stellar halo of the edge-on galaxy NGC 4945. We couple new deep Multi Unit Spectroscopic Explorer spectroscopic observations with existing Hubble Space Telescope imaging data to spectroscopically measure the line-of-sight (LOS) heliocentric velocity and velocity dispersion in two fields at a galactocentric distance of 12.2 kpc (outer disk field) and 34.6 kpc (stellar halo field) along the NGC 4945 major axis, by stacking individual spectra of red giant branch and asymptotic giant branch stars. We obtained a LOS velocity and dispersion of 673 +/- 11 km s(-1) and 73 +/- 14 km s(-1), respectively, for the outer disk field. This is consistent with the mean HI velocity of the disk at that distance. For the halo field, we obtained a LOS velocity and dispersion of 519 +/- 12 km s(-1) and 42 +/- 22 km s(-1). The halo fields' velocity measurement is within similar to 40 km s(-1) from the systemic LOS velocity of NGC 4945, which is 563 km s(-1), suggesting that its stellar halo at 34.6 kpc along the major axis is counter-rotating and its origins are likely to be the result of accretion. This provides the first-ever kinematic measurement of the stellar halo of a Milky Way-mass galaxy outside the Local Group from its resolved stellar population. Thus, we have established a powerful technique for measuring the velocity field for the stellar halos of nearby galaxies.

引用

页数：22