The large- and small-scale Ca II K structure of the Milky Way from observations of Galactic and Magellanic sightlines

ABSTRACT Although highly successful on cosmological scales, cold dark matter (CDM) models predict unobserved overdense ‘cusps’ in dwarf galaxies and overestimate their formation rate. We consider an ultralight axion-like scalar boson which promises to reduce these observational discrepancies at galactic scales. The model, known as fuzzy dark matter (FDM), avoids cusps, suppresses small-scale power, and delays galaxy formation via macroscopic quantum pressure. We compare the substructure and density fluctuations of galactic dark matter haloes comprised of ultralight axions to conventional CDM results. Besides self-gravitating subhaloes, FDM includes non-virialized overdense wavelets formed by quantum interference patterns, which are an efficient source of heating to galactic discs. We find that, in the solar neighbourhood, wavelet heating is sufficient to give the oldest disc stars a velocity dispersion of ${\sim } {30}{\, \mathrm{km\, s}^{-1}}$ within a Hubble time if energy is not lost from the disc, the velocity dispersion increasing with stellar age as σD ∝ t0.4 in agreement with observations. Furthermore, we calculate the radius-dependent velocity dispersion and corresponding scaleheight caused by the heating of this dynamical substructure in both CDM and FDM with the determination that these effects will produce a flaring that terminates the Milky Way disc at $15\!-\!20{\, \mathrm{kpc}}$. Although the source of thickened discs is not known, the heating due to perturbations caused by dark substructure cannot exceed the total disc velocity dispersion. Therefore, this work provides a lower bound on the FDM particle mass of ma > 0.6 × 10−22 eV. Furthermore, FDM wavelets with this particle mass should be considered a viable mechanism for producing the observed disc thickening with time.

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Distance to the nearby dwarf galaxy [TT2009] 25 in the NGC 891 group using the tip of the red giant branch

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936392 ◽

2019 ◽

Vol 629 ◽

pp. L2 ◽

Cited By ~ 1

Author(s):

Oliver Müller ◽

Rodrigo Ibata ◽

Marina Rejkuba ◽

Lorenzo Posti

Keyword(s):

Milky Way ◽

Local Group ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Small Scale ◽

Accurate Information ◽

Standard Candle ◽

Stellar Halo ◽

Red Giant ◽

Small Field Of View

Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. A crucial task is therefore to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, ground-based V and i-band Subaru Suprime Cam photometry with a completeness of i = 27 mag, we measure the distance of the dwarf galaxy [TT2009] 25 using the tip of the red giant branch as a standard candle. This dwarf resides in the field around the Milky Way-analog NGC 891. Using a Bayesian approach, we measure a distance of 10.28−1.73+1.17 Mpc, which is consistent with the distance of NGC 891, and thus confirm it as a member of NGC 891. The dwarf galaxy follows the scaling relations defined by the Local Group dwarfs. We do not find an extended stellar halo around [TT2009] 25. In the small field of view of 100 kpc covered by the survey, only one bright dwarf galaxy and the giant stream are apparent. This is comparable to the Milky Way, where one bright dwarf resides in the same volume, as well as the Sagittarius stream – excluding satellites which are farther away but would be projected in the line-of-sight. It is thus imperative to survey for additional dwarf galaxies in a larger area around NGC 891 to test the abundance of dwarf galaxies and compare this to the number of satellites around the Milky Way.

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The effects of cosmic rays on the formation of Milky Way-mass galaxies in a cosmological context

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1960 ◽

2020 ◽

Vol 497 (2) ◽

pp. 1712-1737 ◽

Cited By ~ 3

Author(s):

Tobias Buck ◽

Christoph Pfrommer ◽

Rüdiger Pakmor ◽

Robert J J Grand ◽

Volker Springel

Keyword(s):

Cosmic Rays ◽

Milky Way ◽

Gamma Ray ◽

Transport Model ◽

Formation Rate ◽

Wave Model ◽

Alfven Wave ◽

Small Scale ◽

Density Peaks ◽

The Impact

ABSTRACT We investigate the impact of cosmic rays (CRs) and different modes of CR transport on the properties of Milky Way-mass galaxies in cosmological magnetohydrodynamical simulations in the context of the AURIGA project. We systematically study how advection, anisotropic diffusion, and additional Alfvén-wave cooling affect the galactic disc and the circumgalactic medium (CGM). Global properties such as stellar mass and star formation rate vary little between simulations with and without various CR transport physics, whereas structural properties such as disc sizes, CGM densities, or temperatures can be strongly affected. In our simulations, CRs affect the accretion of gas on to galaxies by modifying the CGM flow structure. This alters the angular momentum distribution that manifests itself as a difference in stellar and gaseous disc size. The strength of this effect depends on the CR transport model: CR advection results in the most compact discs while the Alfvén-wave model resembles more the AURIGA model. The advection and diffusion models exhibit large (r ∼ 50 kpc) CR pressure-dominated gas haloes causing a smoother and partly cooler CGM. The additional CR pressure smoothes small-scale density peaks and compensates for the missing thermal pressure support at lower CGM temperatures. In contrast, the Alfvén-wave model is only CR pressure dominated at the disc–halo interface and only in this model the gamma-ray emission from hadronic interactions agrees with observations. In contrast to previous findings, we conclude that details of CR transport are critical for accurately predicting the impact of CR feedback on galaxy formation.

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Complexity in small-scale dwarf spheroidal galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s174392131000061x ◽

2009 ◽

Vol 5 (S265) ◽

pp. 227-232

Author(s):

Andreas Koch ◽

Daniel Adén ◽

Eva K. Grebel ◽

Sofia Feltzing

Keyword(s):

Globular Clusters ◽

Milky Way ◽

Galactic Halo ◽

Photometric Data ◽

Small Scale ◽

Chemical Abundance ◽

First Stars ◽

Dwarf Spheroidal Galaxies ◽

Chemical Enrichment ◽

Large Numbers

AbstractOur knowledge about the chemical evolution of the more luminous dwarf spheroidal (dSph) galaxies is constantly growing. However, little is known about the enrichment of the ultrafaint systems recently discovered in large numbers in large Sky Surveys. Low-resolution spectroscopy and photometric data indicate that these galaxies are predominantly metal-poor. On the other hand, the most recent high-resolution abundance analyses indicate that some of these galaxies experienced highly inhomogenous chemical enrichment, where star formation proceeds locally on the smallest scales. Furthermore, these galaxy-contenders appear to contain very metal-poor stars with [Fe/H]< −3 dex and could be the sites of the first stars. Here, we consider the presently available chemical abundance information of the (ultra-) faint Milky Way satellite dSphs. In this context, some of the most peculiar element and inhomogeneous enrichment patterns will be discussed and related to the question of to what extent the faintest dSph candidates and outer halo globular clusters could have contributed to the metal-poor Galactic halo.

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The Warm Gas in the Milky Way: The Kinematical Model of C iv and Its Connection to Si iv

The Astrophysical Journal ◽

10.3847/1538-4357/ac35cd ◽

2022 ◽

Vol 924 (2) ◽

pp. 86

Author(s):

Zhijie Qu ◽

Ryan Lindley ◽

Joel N. Bregman

Keyword(s):

Density Distribution ◽

Milky Way ◽

Galactic Center ◽

Hubble Space Telescope ◽

Density Ratio ◽

Element Abundance ◽

Spatial Density ◽

Small Scale ◽

Relative Extension ◽

Kinematical Model

Abstract We compose a 265-sight-line Milky Way C iv line-shape sample using the Hubble Space Telescope/Cosmic Origins Spectrograph archive, which is complementary to the existing Si iv samples. C iv has a higher ionization potential (47–64 eV) than Si iv (33–45 eV), so it also traces warm gas, which is roughly cospatial with Si iv. The spatial density distribution and kinematics of C iv are identical to those Si iv within ≈2σ. C iv is more sensitive to the warm gas density distribution at large radii with a higher element abundance. Applying the kinematical model to the C iv sample, we find two possible solutions of the density distribution, which are distinguished by the relative extension along the disk midplane and the normal-line direction. Both solutions can reproduce the existing sample and suggest a warm gas disk mass of log M ( M ⊙ ) ≈ 8 and an upper limit of log M ( M ⊙ ) < 9.3 within 250 kpc, which is consistent with Si iv. There is a decrease in the C iv/Si iv column density ratio from the Galactic center to the outskirts by 0.2–0.3 dex, which may suggest a phase transition or different ionization mechanisms for C iv and Si iv. Also, we find that the difference between C iv and Si iv is an excellent tracer of small-scale features, and we find a typical size of 5°–10° for possible turbulence within individual clouds (≈1 kpc).

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From birth associations to field stars: mapping the small-scale orbit distribution in the Galactic disc

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1358 ◽

2020 ◽

Vol 495 (4) ◽

pp. 4098-4112 ◽

Cited By ~ 2

Author(s):

Johanna Coronado ◽

Hans-Walter Rix ◽

Wilma H Trick ◽

Kareem El-Badry ◽

Jan Rybizki ◽

...

Keyword(s):

Main Sequence ◽

Milky Way ◽

Space Distribution ◽

Small Scale ◽

Galactic Disc ◽

Main Sequence Stars ◽

Orbital Phase ◽

Angle Space ◽

Order Of Magnitude ◽

Gaia Dr2

ABSTRACT Stars born at the same time in the same place should have formed from gas of the same element composition. But most stars subsequently disperse from their birth siblings, in orbit and orbital phase, becoming ‘field stars’. Here, we explore and provide direct observational evidence for this process in the Milky Way disc, by quantifying the probability that orbit-similarity among stars implies indistinguishable metallicity. We define the orbit similarity among stars through their distance in action-angle space, Δ(J, θ), and their abundance similarity simply by Δ[Fe/H]. Analysing a sample of main-sequence stars from Gaia DR2 and LAMOST, we find an excess of pairs with the same metallicity (Δ[Fe/H] < 0.1) that extends to remarkably large separations in Δ(J, θ) that correspond to nearly 1 kpc distances. We assess the significance of this effect through a mock sample, drawn from a smooth and phase-mixed orbit distribution. Through grouping such star pairs into associations with a friend-of-friends algorithm linked by Δ(J,θ), we find 100s of mono-abundance groups with ≥3 (to ≳20) members; these groups – some clusters, some spread across the sky – are over an order-of-magnitude more abundant than expected for a smooth phase-space distribution, suggesting that we are witnessing the ‘dissolution’ of stellar birth associations into the field.

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Stellar accelerations and the galactic gravitational field

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2019.25 ◽

2019 ◽

Vol 36 ◽

Cited By ~ 3

Author(s):

Hamish Silverwood ◽

Richard Easther

Keyword(s):

Dark Matter ◽

Milky Way ◽

Precision Measurements ◽

Small Scale ◽

Milky Way Galaxy ◽

Newtonian Dynamics ◽

The Galaxy ◽

Velocity Changes ◽

Blind Search ◽

Stellar Motion

AbstractTypical stars in the Milky Way galaxy have velocities of hundreds of kilometres per second and experience gravitational accelerations of $\sim\!10^{-10}~{\rm m\,s}^{-2}$, resulting in velocity changes of a few centimetres per second over a decade. Measurements of these accelerations would permit direct tests of the applicability of Newtonian dynamics on kiloparsec length scales and could reveal significant small-scale inhomogeneities within the galaxy, as well increasing the sensitivity of measurements of the overall mass distribution of the galaxy. Noting that a reasonable extrapolation of progress in exoplanet hunting spectrographs suggests that centimetre per second level precision will be attainable in the coming decade(s), we explore the possibilities such measurements would create. We consider possible confounding effects, including apparent accelerations induced by stellar motion and reflex velocities from planetary systems, along with possible strategies for their mitigation. If these issues can be satisfactorily addressed, it will be possible to use high-precision measurements of changing stellar velocities to perform a ‘blind search’ for dark matter, make direct tests of theories of non-Newtonian gravitational dynamics, detect local inhomogeneities in the dark matter density, and greatly improve measurements of the overall properties of the galaxy.

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To Observe, or Not to Observe, Quantum-Coherent Dark Matter in the Milky Way, That is a Question

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2021.697140 ◽

2021 ◽

Vol 8 ◽

Author(s):

Tanja Rindler-Daller

Keyword(s):

Dark Matter ◽

Scalar Field ◽

Structure Formation ◽

Cold Dark Matter ◽

Milky Way ◽

Small Scale ◽

Quantum Mechanical ◽

Bose Einstein ◽

The Impact ◽

Observational Signature

In recent years, Bose-Einstein-condensed dark matter (BEC-DM) has become a popular alternative to standard, collisionless cold dark matter (CDM). This BEC-DM -also called scalar field dark matter (SFDM)- can suppress structure formation and thereby resolve the small-scale crisis of CDM for a range of boson masses. However, these same boson masses also entail implications for BEC-DM substructure within galaxies, especially within our own Milky Way. Observational signature effects of BEC-DM substructure depend upon its unique quantum-mechanical features and have the potential to reveal its presence. Ongoing efforts to determine the dark matter substructure in our Milky Way will continue and expand considerably over the next years. In this contribution, we will discuss some of the existing constraints and potentially new ones with respect to the impact of BEC-DM onto baryonic tracers. Studying dark matter substructure in our Milky Way will soon resolve the question, whether dark matter behaves classical or quantum on scales of ≲ 1 kpc.

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GMC Origins and Turbulent Motions in Spiral and Dwarf Galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313000197 ◽

2012 ◽

Vol 8 (S292) ◽

pp. 35-38

Author(s):

Bruce G. Elmegreen

Keyword(s):

High Pressure ◽

Milky Way ◽

Dwarf Galaxies ◽

Scale Structure ◽

Small Scale ◽

Small Scale Structure ◽

Molecule Formation

AbstractCO clouds can be non-self-gravitating in high pressure environments, while most should be strongly self-gravitating at low metallicities and ambient pressures. In the LMC, which is HI-rich, GMC formation and destruction should generally include molecule formation and destruction. In M51, which is CO-rich, GMCs grow by coalescence. The Milky Way is between these two situations. In all cases, large clouds form by accretion of gas and smaller clouds independently of the presence of molecules. GMCs in the Milky Way are analogous to dust lanes and spurs in other galaxies. The virial parameter α usually decreases monotonically with increasing cloud mass in surveys, which implies that small scale structure is formed by turbulence. Hierarchies of sequences with decreasing α should be present in cloud complexes from sub-solar masses up to the ambient Jeans mass (107M⊙).

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The planes of satellite galaxies problem, suggested solutions, and open questions

Modern Physics Letters A ◽

10.1142/s0217732318300045 ◽

2018 ◽

Vol 33 (06) ◽

pp. 1830004 ◽

Cited By ~ 37

Author(s):

Marcel S. Pawlowski

Keyword(s):

Milky Way ◽

Local Group ◽

Small Scale ◽

Velocity Measurements ◽

Cosmological Simulations ◽

Gravitational Effects ◽

Open Questions ◽

Andromeda Galaxy ◽

Satellite Galaxies ◽

Anisotropic Phase

Satellite galaxies of the Milky Way and of the Andromeda galaxy have been found to preferentially align in significantly flattened planes of satellite galaxies, and available velocity measurements are indicative of a preference of satellites in those structures to co-orbit. There is an increasing evidence that such kinematically correlated satellite planes are also present around more distant hosts. Detailed comparisons show that similarly anisotropic phase-space distributions of sub-halos are exceedingly rare in cosmological simulations based on the [Formula: see text]CDM paradigm. Analogs to the observed systems have frequencies of [Formula: see text] 0.5% in such simulations. In contrast to other small-scale problems, the satellite planes issue is not strongly affected by baryonic processes because the distribution of sub-halos on scales of hundreds of kpc is dominated by gravitational effects. This makes the satellite planes one of the most serious small-scale problems for [Formula: see text]CDM. This review summarizes the observational evidence for planes of satellite galaxies in the Local Group and beyond, and provides an overview of how they compare to cosmological simulations. It also discusses scenarios which aim at explaining the coherence of satellite positions and orbits, and why they all are currently unable to satisfactorily resolve the issue.

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