Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSimulations of the Milky Ways central molecular zone -- II. Star formation
116
0
0.0
(
0
)
Added by
Mattia Carlo Sormani
Publication date
2020
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
The Milky Ways central molecular zone (CMZ) has emerged in recent years as a unique laboratory for the study of star formation. Here we use the simulations presented in Tress et al. 2020 to investigate star formation in the CMZ. These simulations resolve the structure of the interstellar medium at sub-parsec resolution while also including the large-scale flow in which the CMZ is embedded. Our main findings are as follows. (1) While most of the star formation happens in the CMZ ring at $Rgtrsim100 {, rm pc}$, a significant amount also occurs closer to SgrA* at $R lesssim 10{, rm pc}$. (2) Most of the star formation in the CMZ happens downstream of the apocentres, consistent with the pearls-on-a-string scenario, and in contrast to the notion that an absolute evolutionary timeline of star formation is triggered by pericentre passage. (3) Within the timescale of our simulations ($sim100$ Myr), the depletion time of the CMZ is constant within a factor of $sim2$. This suggests that variations in the star formation rate are primarily driven by variations in the mass of the CMZ, caused for example by AGN feedback or externally-induced changes in the bar-driven inflow rate, and not by variations in the depletion time. (4) We study the trajectories of newly born stars in our simulations. We find several examples that have age and 3D velocity compatible with those of the Arches and Quintuplet clusters. Our simulations suggest that these prominent clusters originated near the collision sites where the bar-driven inflow accretes onto the CMZ, at symmetrical locations with respect to the Galactic centre, and that they have already decoupled from the gas in which they were born.
rate research
Read More
We use hydrodynamical simulations to study the Milky Ways central molecular zone (CMZ). The simulations include a non-equilibrium chemical network, the gas self-gravity, star formation and supernova feedback. We resolve the structure of the interstellar medium at sub-parsec resolution while also capturing the interaction between the CMZ and the bar-driven large-scale flow out to $Rsim 5kpc$. Our main findings are as follows: (1) The distinction between inner ($Rlesssim120$~pc) and outer ($120lesssim Rlesssim450$~pc) CMZ that is sometimes proposed in the literature is unnecessary. Instead, the CMZ is best described as single structure, namely a star-forming ring with outer radius $Rsimeq 200$~pc which includes the 1.3$^circ$ complex and which is directly interacting with the dust lanes that mediate the bar-driven inflow. (2) This accretion can induce a significant tilt of the CMZ out of the plane. A tilted CMZ might provide an alternative explanation to the $infty$-shaped structure identified in Herschel data by Molinari et al. 2011. (3) The bar in our simulation efficiently drives an inflow from the Galactic disc ($Rsimeq 3$~kpc) down to the CMZ ($Rsimeq200$~pc) of the order of $1rm,M_odot,yr^{-1}$, consistent with observational determinations. (4) Supernova feedback can drive an inflow from the CMZ inwards towards the circumnuclear disc of the order of $sim0.03,rm M_odot,yr^{-1}$. (5) We give a new interpretation for the 3D placement of the 20 and 50 km s$^{-1}$ clouds, according to which they are close ($Rlesssim30$~pc) to the Galactic centre, but are also connected to the larger-scale streams at $Rgtrsim100$~pc.
In this paper we present the CMZoom Surveys catalog of compact sources (< 10, ~0.4pc) within the Central Molecular Zone (CMZ). CMZoom is a Submillimeter Array (SMA) large program designed to provide a complete and unbiased map of all high column density gas (N(H$_2$) $geq$ 10$^{23}$ cm$^{-2}$) of the innermost 500pc of the Galaxy in the 1.3mm dust continuum. We generate both a robust catalog designed to reduce spurious source detections, and a second catalog with higher completeness, both generated using a pruned dendrogram. In the robust catalog, we report 285 compact sources, or 816 in the high completeness catalog. These sources have effective radii between 0.04-0.4 pc, and are the potential progenitors of star clusters. The masses for both catalogs are dominated by the Sagittarius B2 cloud complex, where masses are likely unreliable due to free-free contamination, uncertain dust temperatures, and line-of-sight confusion. Given the survey selection and completeness, we predict that our robust catalog accounts for more than ~99% of compact substructure capable of forming high mass stars in the CMZ. This catalog provides a crucial foundation for future studies of high-mass star formation in the Milky Ways Galactic Center.
We present spatially resolved imaging and integral field spectroscopy data for 450 cool giant stars within 1,pc from Sgr,A*. We use the prominent CO bandheads to derive effective temperatures of individual giants. Additionally we present the deepest spectroscopic observation of the Galactic Center so far, probing the number of B9/A0 main sequence stars ($2.2-2.8,M_odot$) in two deep fields. From spectro-photometry we construct a Hertzsprung-Russell diagram of the red giant population and fit the observed diagram with model populations to derive the star formation history of the nuclear cluster. We find that (1) the average nuclear star-formation rate dropped from an initial maximum $sim10$,Gyrs ago to a deep minimum 1-2,Gyrs ago and increased again during the last few hundred Myrs, and (2) that roughly 80% of the stellar mass formed more than 5,Gyrs ago; (3) mass estimates within $rm Rsim1,pc$ from Sgr,A* favor a dominant star formation mode with a normal Chabrier/Kroupa initial mass function for the majority of the past star formation in the Galactic Center. The bulk stellar mass seems to have formed under conditions significantly different from the young stellar disks, perhaps because at the time of the formation of the nuclear cluster the massive black hole and its sphere of influence was much smaller than today.
The stellar populations in the inner kiloparsecs of the Milky Way (MW) show complex kinematical and chemical structures. The origin and evolution of these structures is still under debate. Here we study the central region of a fully cosmological hydrodynamical simulation of a disk galaxy that reproduces key properties of the inner kiloparsecs of the MW: it has a boxy morphology and shows an overall rotation and dispersion profile in agreement with observations. We use a clustering algorithm on stellar kinematics to identify a number of discrete kinematic components: a high- and low-spin disk, a stellar halo and two bulge components; one fast rotating and one slow-rotating. We focus on the two bulge components and show that the slow rotating one is spherically symmetric while the fast rotating component shows a boxy/peanut morphology. Although the two bulge components are kinematically discrete populations at present-day, they are both mostly formed over similar time scales, from disk material. We find that stellar particles with lower initial birth angular momentum (most likely thick disc stars) end up in the slow-rotating low-spin bulge, while stars with higher birth angular momentum (most likely thin disc stars) are found in the high-spin bulge. This has the important consequence that a bulge population with a spheroidal morphology does not necessarily indicate a merger origin. In fact, we do find that only $sim2.3$% of the stars in the bulge components are ex-situ stars brought in by accreted dwarf galaxies early on. We identify these ex-situ stars as the oldest and most metal-poor stars on highly radial orbits with large vertical excursions from the disk.
The nuclear stellar disc (NSD) is, together with the nuclear star cluster (NSC) and the central massive black hole, one of the main components in the central parts of our Milky Way. However, until recently, only few studies of the stellar content of the NSD have been obtained due to extreme extinction and stellar crowding. With a dedicated KMOS (VLT, ESO) spectroscopic survey, we study the kinematics and global metallicities of the NSD based on the observations of K/M giant stars. We trace radial velocities and metallicities which were derived based on spectral indices (Na I and CO) along the NSD and compare those with a Galactic Bulge sample of APOGEE (DR16) and data from the NSC. We find that the metallicity distribution function and the fraction of metal-rich and metal-poor stars in the NSD are different from the corresponding distributions and ratios of the NSC and the Galactic Bulge. By tracing the velocity dispersion as a function of metallicity, we clearly see that the NSD is kinematically cool and that the velocity dispersion decreases with increasing metallicity contrary to the inner Bulge sample of APOGEE ($rm |b| < 4^{o}$). Using molecular gas tracers ($rm H_{2}CO$, CO(4-3)) of the Central Molecular Zone (CMZ) we find an astonishing agreement between the gas rotation and the rotation of the metal-rich population indicating that the metal-rich stars could have formed from gas in the CMZ. On the other hand, the metal-poor stars show a much slower rotation profile with signs of counter-rotation indicating a different origin of these stars. Coupling kinematics with global metallicities, our results demonstrate that the NSD is chemically and kinematically distinct with respect to the inner Bulge indicating a different formation scenario.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
