Painting a portrait of the Galactic disc with its stellar clusters

Context. The large astrometric and photometric survey performed by the Gaia mission allows for a panoptic view of the Galactic disc and its stellar cluster population. Hundreds of stellar clusters were only discovered after the latest Gaia data release (DR2) and have yet to be characterised. Aims. Here we make use of the deep and homogeneous Gaia photometry down to G = 18 to estimate the distance, age, and interstellar reddening for about 2000 stellar clusters identified with Gaia DR2 astrometry. We use these objects to study the structure and evolution of the Galactic disc. Methods. We relied on a set of objects with well-determined parameters in the literature to train an artificial neural network to estimate parameters from the Gaia photometry of cluster members and their mean parallax. Results. We obtain reliable parameters for 1867 clusters. Our catalogue confirms the relative lack of old stellar clusters in the inner disc (with a few notable exceptions). We also quantify and discuss the variation of scale height with cluster age, and we detect the Galactic warp in the distribution of old clusters. Conclusions. This work results in a large and homogeneous cluster catalogue, allowing one to trace the structure of the disc out to distances of ∼4 kpc. However, the present sample is still unable to trace the outer spiral arm of the Milky Way, which indicates that the outer disc cluster census might still be incomplete.

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Distribution and kinematics of 26Al in the Galactic disc

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2125 ◽

2020 ◽

Vol 497 (2) ◽

pp. 2442-2454 ◽

Cited By ~ 2

Author(s):

Yusuke Fujimoto ◽

Mark R Krumholz ◽

Shu-ichiro Inutsuka

Keyword(s):

Star Formation ◽

Milky Way ◽

Spiral Structure ◽

Rotation Speed ◽

Scale Height ◽

Stellar Winds ◽

Galactic Disc ◽

Stellar Feedback ◽

Self Gravity ◽

Solar Position

ABSTRACT 26Al is a short-lived radioactive isotope thought to be injected into the interstellar medium (ISM) by massive stellar winds and supernovae (SNe). However, all-sky maps of 26Al emission show a distribution with a much larger scale height and faster rotation speed than either massive stars or the cold ISM. We investigate the origin of this discrepancy using an N-body + hydrodynamics simulation of a Milky-Way-like galaxy, self-consistently including self-gravity, star formation, stellar feedback, and 26Al production. We find no evidence that the Milky Way’s spiral structure explains the 26Al anomaly. Stars and the 26Al bubbles they produce form along spiral arms, but, because our simulation produces material arms that arise spontaneously rather than propagating arms forced by an external potential, star formation occurs at arm centres rather than leading edges. As a result, we find a scale height and rotation speed for 26Al similar to that of the cold ISM. However, we also show that a synthetic 26Al emission map produced for a possible Solar position at the edge of a large 26Al bubble recovers many of the major qualitative features of the observed 26Al sky. This suggests that the observed anomalous 26Al distribution is the product of foreground emission from the 26Al produced by a nearby, recent SN.

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Mapping the Galactic disc with the LAMOST and Gaia red clump sample: II. 3D asymmetrical kinematics of mono-age populations in the disc between 6–14 kpc

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3113 ◽

2019 ◽

Vol 491 (2) ◽

pp. 2104-2118 ◽

Cited By ~ 4

Author(s):

H-F Wang ◽

M López-Corredoira ◽

Y Huang ◽

J L Carlin ◽

B-Q Chen ◽

...

Keyword(s):

Milky Way ◽

Galactic Disc ◽

Giant Stars ◽

Bending Mode ◽

Red Clump ◽

Minor Mergers ◽

Gaia Dr2 ◽

South Asymmetry ◽

Spiral Arm ◽

Fast Rotating

ABSTRACT We perform analysis of the 3D kinematics of Milky Way disc stars in mono-age populations. We focus on stars between Galactocentric distances of R = 6 and 14 kpc, selected from the combined LAMOST Data Release 4 (DR4) red clump giant stars and Gaia DR2 proper motion catalogue. We confirm the 3D asymmetrical motions of recent works and provide time tagging of the Galactic outer disc asymmetrical motions near the anticentre direction out to Galactocentric distances of 14 kpc. Radial Galactocentric motions reach values up to 10 km s−1, depending on the age of the population, and present a north–south asymmetry in the region corresponding to density and velocity substructures that were sensitive to the perturbations in the early 6 Gyr. After that time, the disc stars in this asymmetrical structure have become kinematically hotter, and are thus not sensitive to perturbations, and we find the structure is a relatively younger population. With quantitative analysis, we find stars both above and below the plane at R ≳ 9 kpc that exhibit bending mode motions of which the sensitive duration is around 8 Gyr. We speculate that the in-plane asymmetries might not be mainly caused by a fast rotating bar, intrinsically elliptical outer disc, secular expansion of the disc, or streams. Spiral arm dynamics, out-of-equilibrium models, minor mergers or others are important contributors. Vertical motions might be dominated by bending and breathing modes induced by complicated inner or external perturbers. It is likely that many of these mechanisms are coupled together.

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The ecology of the galactic centre: Nuclear stellar clusters and supermassive black holes

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319006689 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 80-83 ◽

Cited By ~ 1

Author(s):

Melvyn B. Davies ◽

Abbas Askar ◽

Ross P. Church

Keyword(s):

Black Holes ◽

Black Hole ◽

Large Fraction ◽

Galactic Nuclei ◽

Supermassive Black Holes ◽

Galactic Centre ◽

Stellar Clusters ◽

Stellar Cluster ◽

Supermassive Black Hole ◽

Multiple Clusters

AbstractSupermassive black holes are found in most galactic nuclei. A large fraction of these nuclei also contain a nuclear stellar cluster surrounding the black hole. Here we consider the idea that the nuclear stellar cluster formed first and that the supermassive black hole grew later. In particular we consider the merger of three stellar clusters to form a nuclear stellar cluster, where some of these clusters contain a single intermediate-mass black hole (IMBH). In the cases where multiple clusters contain IMBHs, we discuss whether the black holes are likely to merge and whether such mergers are likely to result in the ejection of the merged black hole from the nuclear stellar cluster. In some cases, no supermassive black hole will form as any merger product is not retained. This is a natural pathway to explain those galactic nuclei that contain a nuclear stellar cluster but apparently lack a supermassive black hole; M33 being a nearby example. Alternatively, if an IMBH merger product is retained within the nuclear stellar cluster, it may subsequently grow, e.g. via the tidal disruption of stars, to form a supermassive black hole.

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Radial metallicity gradients with Galactic nebular probes

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319004150 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 240-241 ◽

Cited By ~ 1

Author(s):

Jorge García-Rojas

Keyword(s):

Milky Way ◽

Galactic Disc ◽

Formation And Evolution

AbstractThe study of radial metallicity gradients in the disc of the Milky Way is a powerful tool to understand the mechamisms that have been acting in the formation and evolution of the Galactic disc. In this proceeding, I will put the eye on some problems that should be carefully addressed to obtain precise determinations of the metallicity gradients.

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Structure of the Milky Way and the distribution of young stellar clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307008083 ◽

2006 ◽

Vol 2 (S241) ◽

Author(s):

Maria Messineo ◽

Karl M. Menten ◽

Harm J. Habing ◽

Monika Petr-Gotzens ◽

Frédéric Schuller

Keyword(s):

Milky Way ◽

Stellar Clusters

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Formation of supermassive black holes in galactic nuclei – I. Delivering seed intermediate-mass black holes in massive stellar clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab113 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2682-2700

Author(s):

Abbas Askar ◽

Melvyn B Davies ◽

Ross P Church

Keyword(s):

Black Holes ◽

Galactic Nuclei ◽

Supermassive Black Holes ◽

Stellar Clusters ◽

Orbital Eccentricity ◽

Intermediate Mass ◽

Stellar Cluster ◽

Wave Emission ◽

Gas Accretion ◽

Intermediate Mass Black Holes

ABSTRACT Supermassive black holes (SMBHs) are found in most galactic nuclei. A significant fraction of these nuclei also contains a nuclear stellar cluster (NSC) surrounding the SMBH. In this paper, we consider the idea that the NSC forms first, from the merger of several stellar clusters that may contain intermediate-mass black holes (IMBHs). These IMBHs can subsequently grow in the NSC and form an SMBH. We carry out N-body simulations of the simultaneous merger of three stellar clusters to form an NSC, and investigate the outcome of simulated runs containing zero, one, two, and three IMBHs. We find that IMBHs can efficiently sink to the centre of the merged cluster. If multiple merging clusters contain an IMBH, we find that an IMBH binary is likely to form and subsequently merge by gravitational wave emission. We show that these mergers are catalyzed by dynamical interactions with surrounding stars, which systematically harden the binary and increase its orbital eccentricity. The seed SMBH will be ejected from the NSC by the recoil kick produced when two IMBHs merge, if their mass ratio q ≳ 0.15. If the seed is ejected then no SMBH will form in the NSC. This is a natural pathway to explain those galactic nuclei that contain an NSC but apparently lack an SMBH, such as M33. However, if an IMBH is retained then it can seed the growth of an SMBH through gas accretion and tidal disruption of stars.

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Is High-Velocity Cloud Complex C Associated with the Galactic Warp?

Publications of the Astronomical Society of Australia ◽

10.1071/as03028 ◽

2003 ◽

Vol 20 (3) ◽

pp. 263-269 ◽

Cited By ~ 4

Author(s):

Daisuke Kawata ◽

Christopher Thom ◽

Brad K. Gibson

Keyword(s):

High Latitude ◽

High Velocity ◽

Large Magellanic Cloud ◽

Alternative Interpretation ◽

North Polar ◽

Gas Cloud ◽

Cloud Complex ◽

Galactic Warp ◽

Velocity Cloud ◽

Spiral Arm

AbstractWe test the hypothesis that high-velocity gas cloud Complex C is actually a high-latitude spiral arm extension in the direction of the Galactic warp, as opposed to the standard interpretation — that of a once extragalactic, but now infalling, gas cloud. A parallel Tree N-body code was employed to simulate the tidal interaction of a satellite perturber with the Milky Way. We find that a model incorporating a perturber of the mass of the Large Magellanic Cloud on a south to north polar orbit, crossing the disk at ˜15 kpc, does yield a high-velocity, high-latitude extension consistent with the spatial, kinematical, and column density properties of Complex C. Unless this massive satellite remains undiscovered because of either a fortuitous alignment with the Galactic bulge (feasible within the framework of the model), or the lack of any associated baryonic component, we conclude that this alternative interpretation appears unlikely.

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A Kiloparsec-scale Molecular Wave in the Inner Galaxy: Feather of the Milky Way?

The Astrophysical Journal ◽

10.3847/2041-8213/ac341f ◽

2021 ◽

Vol 921 (2) ◽

pp. L42

Author(s):

V. S. Veena ◽

P. Schilke ◽

Á. Sánchez-Monge ◽

M. C. Sormani ◽

R. S. Klessen ◽

...

Keyword(s):

Molecular Structure ◽

Aspect Ratio ◽

Milky Way ◽

Spiral Galaxies ◽

Galactic Center ◽

Velocity Data ◽

Sinusoidal Wave ◽

Angular Extent ◽

The Vertical Distribution ◽

Spiral Arm

Abstract We report the discovery of a velocity coherent, kiloparsec-scale molecular structure toward the Galactic center region with an angular extent of 30° and an aspect ratio of 60:1. The kinematic distance of the CO structure ranges between 4.4 and 6.5 kpc. Analysis of the velocity data and comparison with the existing spiral arm models support that a major portion of this structure is either a subbranch of the Norma arm or an interarm giant molecular filament, likely to be a kiloparsec-scale feather (or spur) of the Milky Way, similar to those observed in nearby spiral galaxies. The filamentary cloud is at least 2.0 kpc in extent, considering the uncertainties in the kinematic distances, and it could be as long as 4 kpc. The vertical distribution of this highly elongated structure reveals a pattern similar to that of a sinusoidal wave. The exact mechanisms responsible for the origin of such a kiloparsec-scale filament and its wavy morphology remains unclear. The distinct wave-like shape and its peculiar orientation makes this cloud, named as the Gangotri wave, one of the largest and most intriguing structures identified in the Milky Way.

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Autonomous Gaussian decomposition of the Galactic Ring Survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038479 ◽

2020 ◽

Vol 640 ◽

pp. A72

Author(s):

M. Riener ◽

J. Kainulainen ◽

J. D. Henshaw ◽

H. Beuther

Keyword(s):

Milky Way ◽

Velocity Dispersion ◽

Galactic Plane ◽

Gas Emission ◽

Spiral Arms ◽

Precise Knowledge ◽

Significant Difference ◽

The Impact ◽

Co Emission ◽

Spiral Arm

Knowledge about the distribution of CO emission in the Milky Way is essential to understanding the impact of the Galactic environment on the formation and evolution of structures in the interstellar medium. However, our current insight as to the fraction of CO in the spiral arm and interarm regions is still limited by large uncertainties in assumed rotation curve models or distance determination techniques. In this work we use the Bayesian approach from Reid et al. (2016, ApJ, 823, 77; 2019, ApJ, 885, 131), which is based on our most precise knowledge at present about the structure and kinematics of the Milky Way, to obtain the current best assessment of the Galactic distribution of 13CO from the Galactic Ring Survey. We performed two different distance estimates that either included (Run A) or excluded (Run B) a model for Galactic features, such as spiral arms or spurs. We also included a prior for the solution of the kinematic distance ambiguity that was determined from a compilation of literature distances and an assumed size-linewidth relationship. Even though the two distance runs show strong differences due to the prior for Galactic features for Run A and larger uncertainties due to kinematic distances in Run B, the majority of their distance results are consistent with each other within the uncertainties. We find that the fraction of 13CO emission associated with spiral arm features ranges from 76 to 84% between the two distance runs. The vertical distribution of the gas is concentrated around the Galactic midplane, showing full-width at half-maximum values of ~75 pc. We do not find any significant difference between gas emission properties associated with spiral arm and interarm features. In particular, the distribution of velocity dispersion values of gas emission in spurs and spiral arms is very similar. We detect a trend of higher velocity dispersion values with increasing heliocentric distance, which we, however, attribute to beam averaging effects caused by differences in spatial resolution. We argue that the true distribution of the gas emission is likely more similar to a combination of the two distance results discussed, and we highlight the importance of using complementary distance estimations to safeguard against the pitfalls of any single approach. We conclude that the methodology presented in this work is a promising way to determine distances to gas emission features in Galactic plane surveys.

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