Towards a fully consistent Milky Way disk model. IV. The impact of Gaia DR2 and APOGEE

Abstract We study the effects of inelastic dark matter self-interactions on the internal structure of a simulated Milky Way (MW)-size halo. Self-interacting dark matter (SIDM) is an alternative to collisionless cold dark matter (CDM) which offers a unique solution to the problems encountered with CDM on sub-galactic scales. Although previous SIDM simulations have mainly considered elastic collisions, theoretical considerations motivate the existence of multi-state dark matter where transitions from the excited to the ground state are exothermic. In this work, we consider a self-interacting, two-state dark matter model with inelastic collisions, implemented in the Arepo code. We find that energy injection from inelastic self-interactions reduces the central density of the MW halo in a shorter timescale relative to the elastic scale, resulting in a larger core size. Inelastic collisions also isotropize the orbits, resulting in an overall lower velocity anisotropy for the inelastic MW halo. In the inner halo, the inelastic SIDM case (minor-to-major axis ratio s ≡ c/a ≈ 0.65) is more spherical than the CDM (s ≈ 0.4), but less spherical than the elastic SIDM case (s ≈ 0.75). The speed distribution f(v) of dark matter particles at the location of the Sun in the inelastic SIDM model shows a significant departure from the CDM model, with f(v) falling more steeply at high speeds. In addition, the velocity kicks imparted during inelastic collisions produce unbound high-speed particles with velocities up to 500 km s−1 throughout the halo. This implies that inelastic SIDM can potentially leave distinct signatures in direct detection experiments, relative to elastic SIDM and CDM.

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A Gaia DR2 view of the open cluster population in the Milky Way

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833476 ◽

2018 ◽

Vol 618 ◽

pp. A93 ◽

Cited By ~ 180

Author(s):

T. Cantat-Gaudin ◽

C. Jordi ◽

A. Vallenari ◽

A. Bragaglia ◽

L. Balaguer-Núñez ◽

...

Keyword(s):

Stellar Evolution ◽

Milky Way ◽

Galactic Plane ◽

Galactic Disk ◽

Open Cluster ◽

Open Clusters ◽

Number Of Clusters ◽

History Of ◽

Gaia Dr2

Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.

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Gaia DR2 proper motions of dwarf galaxies within 420 kpc

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833343 ◽

2018 ◽

Vol 619 ◽

pp. A103 ◽

Cited By ~ 94

Author(s):

T. K. Fritz ◽

G. Battaglia ◽

M. S. Pawlowski ◽

N. Kallivayalil ◽

R. van der Marel ◽

...

Keyword(s):

Milky Way ◽

Dwarf Galaxies ◽

High Mass ◽

Proper Motions ◽

Proper Understanding ◽

Satellite Problem ◽

Cosmological Context ◽

Good Consistency ◽

Gaia Dr2 ◽

Limited Accuracy

A proper understanding of the Milky Way (MW) dwarf galaxies in a cosmological context requires knowledge of their 3D velocities and orbits. However, proper motion (PM) measurements have generally been of limited accuracy and are available only for more massive dwarfs. We therefore present a new study of the kinematics of the MW dwarf galaxies. We use the Gaia DR2 for those dwarfs that have been spectroscopically observed in the literature. We derive systemic PMs for 39 galaxies and galaxy candidates out to 420 kpc, and generally find good consistency for the subset with measurements available from other studies. We derive the implied Galactocentric velocities, and calculate orbits in canonical MW halo potentials of low (0.8 × 1012 M⊙) and high mass (1.6 × 1012 M⊙). Comparison of the distributions of orbital apocenters and 3D velocities to the halo virial radius and escape velocity, respectively, suggests that the satellite kinematics are best explained in the high-mass halo. Tuc III, Crater II, and additional candidates have orbital pericenters small enough to imply significant tidal influences. Relevant to the missing satellite problem, the fact that fewer galaxies are observed to be near apocenter than near pericenter implies that there must be a population of distant dwarf galaxies yet to be discovered. Of the 39 dwarfs: 12 have orbital poles that do not align with the MW plane of satellites (given reasonable assumptions about its intrinsic thickness); 10 have insufficient PM accuracy to establish whether they align; and 17 satellites align, of which 11 are co-orbiting and (somewhat surprisingly, in view of prior knowledge) 6 are counter-orbiting. Group infall might have contributed to this, but no definitive association is found for the members of the Crater-Leo group.

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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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The Milky Way Cepheid Leavitt law based on Gaia DR2 parallaxes of companion stars and host open cluster populations

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038633 ◽

2020 ◽

Vol 643 ◽

pp. A115 ◽

Cited By ~ 1

Author(s):

Louise Breuval ◽

Pierre Kervella ◽

Richard I. Anderson ◽

Adam G. Riess ◽

Frédéric Arenou ◽

...

Keyword(s):

Milky Way ◽

Open Cluster ◽

Hubble Constant ◽

Zero Point ◽

Spatially Resolved ◽

Trigonometric Parallax ◽

Novel Approach ◽

Classical Cepheids ◽

Average Cluster ◽

Gaia Dr2

Aims. Classical Cepheids provide the foundation for the empirical extragalactic distance ladder. Milky Way Cepheids are the only stars in this class accessible to trigonometric parallax measurements. However, the parallaxes of Cepheids from the second Gaia data release (GDR2) are affected by systematics because of the absence of chromaticity correction, and occasionally by saturation. Methods. As a proxy for the parallaxes of 36 Galactic Cepheids, we adopt either the GDR2 parallaxes of their spatially resolved companions or the GDR2 parallax of their host open cluster. This novel approach allows us to bypass the systematics on the GDR2 Cepheids parallaxes that is induced by saturation and variability. We adopt a GDR2 parallax zero-point (ZP) of −0.046 mas with an uncertainty of 0.015 mas that covers most of the recent estimates. Results. We present new Galactic calibrations of the Leavitt law in the V, J, H, KS, and Wesenheit WH bands. We compare our results with previous calibrations based on non-Gaia measurements and compute a revised value for the Hubble constant anchored to Milky Way Cepheids. Conclusions. From an initial Hubble constant of 76.18 ± 2.37 km s−1 Mpc−1 based on parallax measurements without Gaia, we derive a revised value by adopting companion and average cluster parallaxes in place of direct Cepheid parallaxes, and we find H0 = 72.8 ± 1.9 (statistical + systematics) ±1.9 (ZP) km s−1 Mpc−1 when all Cepheids are considered and H0 = 73.0 ± 1.9 (statistical + systematics) ±1.9 (ZP) km s−1 Mpc−1 for fundamental mode pulsators only.

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Interpreting high spatial resolution line observations of planet-forming disks with gaps and rings: the case of HD 163296

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038712 ◽

2020 ◽

Vol 642 ◽

pp. A165

Author(s):

Ch. Rab ◽

I. Kamp ◽

C. Dominik ◽

C. Ginski ◽

G. A. Muro-Arena ◽

...

Keyword(s):

Spatial Resolution ◽

High Spatial Resolution ◽

Line Emission ◽

High Angular Resolution ◽

Back Side ◽

Gas Temperature ◽

Disk Model ◽

Gas Density ◽

The Impact ◽

Gas Properties

Context. Spatially resolved continuum observations of planet-forming disks show prominent ring and gap structures in their dust distribution. However, the picture from gas observations is much less clear and constraints on the radial gas density structure (i.e. gas gaps) remain rare and uncertain. Aims. We want to investigate the importance of thermo-chemical processes for the interpretation of high-spatial-resolution gas observations of planet-forming disks and their impact on the derived gas properties. Methods. We applied the radiation thermo-chemical disk code PRODIMO (PROtoplanetary DIsk MOdel) to model the dust and gas disk of HD 163296 self-consistently, using the DSHARP (Disk Substructure at High Angular Resolution) gas and dust observations. With this model we investigated the impact of dust gaps and gas gaps on the observables and the derived gas properties, considering chemistry, and heating and cooling processes. Results. We find distinct peaks in the radial line intensity profiles of the CO line data of HD 163296 at the location of the dust gaps. Our model indicates that those peaks are not only a consequence of a gas temperature increase within the gaps but are mainly caused by the absorption of line emission from the back side of the disk by the dust rings. For two of the three prominent dust gaps in HD 163296, we find that thermo-chemical effects are negligible for deriving density gradients via measurements of the rotation velocity. However, for the gap with the highest dust depletion, the temperature gradient can be dominant and needs to be considered to derive accurate gas density profiles. Conclusions. Self-consistent gas and dust thermo-chemical modelling in combination with high-quality observations of multiple molecules are necessary to accurately derive gas gap depths and shapes. This is crucial to determine the origin of gaps and rings in planet-forming disks and to improve the mass estimates of forming planets if they are the cause of the gap.

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The escape speed curve of the Galaxy obtained from Gaia DR2 implies a heavy Milky Way

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833748 ◽

2018 ◽

Vol 616 ◽

pp. L9 ◽

Cited By ~ 41

Author(s):

G. Monari ◽

B. Famaey ◽

I. Carrillo ◽

T. Piffl ◽

M. Steinmetz ◽

...

Keyword(s):

Mass Concentration ◽

Milky Way ◽

Galactic Centre ◽

High Concentration ◽

Circular Velocity ◽

Halo Stars ◽

Dark Matter Mass ◽

The Galaxy ◽

Escape Speed ◽

Gaia Dr2

We measure the escape speed curve of the Milky Way based on the analysis of the velocity distribution of ~2850 counter-rotating halo stars from the Gaia Data Release 2. The distances were estimated through the StarHorse code, and only stars with distance errors smaller than 10% were used in the study. The escape speed curve is measured at Galactocentric radii ranging from ~5 kpc to ~10.5 kpc. The local Galactic escape at the Sun’s position is estimated to be ve(r⊙) = 580 ± 63 km s−1, and it rises towards the Galactic centre. Defined as the minimum speed required to reach three virial radii, our estimate of the escape speed as a function of radius implies for a Navarro–Frenk–White profile and local circular velocity of 240 km s−1 a dark matter mass M200 = 1.28−0.50+0.68 × 1012 M⊙ and a high concentration c200 = 11.09−1.79+2.94. Assuming the mass-concentration relation of ΛCDM, we obtain M200 = 1.55−0.51+0.64 × 1012 M⊙ and c200 = 7.93−0.27+0.33 for a local circular velocity of 228 km s−1.

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High reddening patches in Gaia DR2

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936881 ◽

2020 ◽

Vol 634 ◽

pp. A33

Author(s):

Leire Beitia-Antero ◽

Ana Inés Gómez de Castro ◽

Raúl de la Fuente Marcos

Keyword(s):

Star Formation ◽

Milky Way ◽

Spectroscopic Analysis ◽

Galactic Halo ◽

Spiral Galaxies ◽

Monte Carlo Sampling ◽

The Other ◽

Host Galaxies ◽

Galactic Model ◽

Gaia Dr2

Context. Deep GALEX UV data show that the extreme outskirts of some spiral galaxies are teeming with star formation. Such young stellar populations evolving so far away from the bulk of their host galaxies challenge our overall understanding of how star formation proceeds at galactic scales. It is at present unclear whether our own Milky Way may also exhibit ongoing and recent star formation beyond the conventional edge of the disk (∼15 kpc). Aims. Using Gaia DR2 data, we aim to determine if such a population is present in the Galactic halo, beyond the nominal radius of the Milky Way disk. Methods. We studied the kinematics of Gaia DR2 sources with parallax values between 1/60 and 1/30 milliarcseconds towards two regions that show abnormally high values of extinction and reddening; the results are compared with predictions from GALAXIA Galactic model. We also plotted the color–magnitude (CM) diagrams with heliocentric distances computed inverting the parallaxes, and studied the effects of the large parallax errors by Monte Carlo sampling. Results. The kinematics point towards a Galactic origin for one of the regions, while the provenance of the stars in the other is not clear. A spectroscopic analysis of some of the sources in the first region confirms that they are located in the halo. The CM diagram of the sources suggests that some of them are young.

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Predictably missing satellites: subhalo abundances in Milky Way-like haloes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1098 ◽

2019 ◽

Vol 486 (4) ◽

pp. 4545-4568 ◽

Cited By ~ 5

Author(s):

Catherine E Fielder ◽

Yao-Yuan Mao ◽

Jeffrey A Newman ◽

Andrew R Zentner ◽

Timothy C Licquia

Keyword(s):

Dark Matter ◽

Confidence Level ◽

Mass Concentration ◽

Cold Dark Matter ◽

Milky Way ◽

Scale Factor ◽

Magellanic Clouds ◽

Small Scales ◽

Major Merger ◽

The Impact

ABSTRACT On small scales there have been a number of claims of discrepancies between the standard cold dark matter (CDM) model and observations. The ‘missing satellites problem’ infamously describes the overabundance of subhaloes from CDM simulations compared to the number of satellites observed in the Milky Way. A variety of solutions to this discrepancy have been proposed; however, the impact of the specific properties of the Milky Way halo relative to the typical halo of its mass has yet to be explored. Motivated by recent studies that identified ways in which the Milky Way is atypical, we investigate how the properties of dark matter haloes with mass comparable to our Galaxy’s – including concentration, spin, shape, and scale factor of the last major merger – correlate with the subhalo abundance. Using zoom-in simulations of Milky Way-like haloes, we build two models of subhalo abundance as functions of host halo properties. From these models we conclude that the Milky Way most likely has fewer subhaloes than the average halo of the same mass. We expect up to 30 per cent fewer subhaloes with low maximum rotation velocities ($V_{\rm max}^{\rm sat} \sim 10$ km s−1) at the 68 per cent confidence level and up to 52 per cent fewer than average subhaloes with high rotation velocities ($V_{\rm max}^{\rm sat} \gtrsim 30$ km s−1, comparable to the Magellanic Clouds) than would be expected for a typical halo of the Milky Way’s mass. Concentration is the most informative single parameter for predicting subhalo abundance. Our results imply that models tuned to explain the missing satellites problem assuming typical subhalo abundances for our Galaxy may be overcorrecting.

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The mass of our Galaxy from satellite proper motions in the Gaia era

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1040 ◽

2020 ◽

Vol 494 (4) ◽

pp. 5178-5193 ◽

Cited By ~ 5

Author(s):

T K Fritz ◽

A Di Cintio ◽

G Battaglia ◽

C Brook ◽

S Taibi

Keyword(s):

Milky Way ◽

Anisotropy Parameter ◽

Large Magellanic Cloud ◽

Mass Determination ◽

Proper Motions ◽

Radial Density ◽

Full Sample ◽

Scale Free ◽

Virial Mass ◽

Gaia Dr2

ABSTRACT We use Gaia DR2 systemic proper motions of 45 satellite galaxies to constrain the mass of the Milky Way using the scale-free mass estimator of Watkins et al. (2010). We first determine the anisotropy parameter β, and the tracer satellites’ radial density index γ to be β = $-0.67^{+0.45}_{-0.62}$ and γ = 2.11 ± 0.23. When we exclude possible former satellites of the Large Magellanic Cloud, the anisotropy changes to β = $-0.21^{+0.37}_{-0.51}$. We find that the index of the Milky Way’s gravitational potential α, which is dependent on the mass itself, is the parameter with the largest impact on the mass determination. Via comparison with cosmological simulations of Milky Way-like galaxies, we carried out a detailed analysis of the estimation of the observational uncertainties and their impact on the mass estimator. We found that the mass estimator is biased when applied naively to the satellites of simulated Milky Way haloes. Correcting for this bias, we obtain for our Galaxy a mass of $0.58^{+0.15}_{-0.14}\times 10^{12}$ M⊙ within 64 kpc, as computed from the inner half of our observational sample, and $1.43^{+0.35}_{-0.32}\times 10^{12}$ M⊙ within 273 kpc, from the full sample; this latter value extrapolates to a virial mass of $M_\mathrm{vir\, \Delta =97}=1.51^{+0.45}_{-0.40} \times 10^{12}\,{\rm M}_{\odot }$ corresponding to a virial radius of Rvir = 308 ± 29 kpc. This value of the Milky Way mass lies in-between other mass estimates reported in the literature, from various different methods.

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