scholarly journals The MUSE-Faint survey

2020 ◽  
Vol 635 ◽  
pp. A107
Author(s):  
Sebastiaan L. Zoutendijk ◽  
Jarle Brinchmann ◽  
Leindert A. Boogaard ◽  
Madusha L. P. Gunawardhana ◽  
Tim-Oliver Husser ◽  
...  
Keyword(s):  
Dark Matter ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Mass Range ◽  
Line Of Sight ◽  
Large Telescope ◽  
Stellar Cluster ◽  
Set Constraints ◽  
Very Large Telescope ◽  
Intrinsic Mean

Aims. It has been shown that the ultra-faint dwarf galaxy Eridanus 2 may host a stellar cluster in its centre. If this cluster is shown to exist, it can be used to set constraints on the mass and abundance of massive astrophysical compact halo objects (MACHOs) as a form of dark matter. Previous research has shown promising expectations in the mass range of 10−100 M⊙, but lacked spectroscopic measurements of the cluster. We aim to provide spectroscopic evidence regarding the nature of the putative star cluster in Eridanus 2 and to place constraints on MACHOs as a constituent of dark matter. Methods. We present spectroscopic observations of the central square arcminute of Eridanus 2 from MUSE-Faint, a survey of ultra-faint dwarf galaxies with the Multi Unit Spectroscopic Explorer on the Very Large Telescope. We derived line-of-sight velocities for possible member stars of the putative cluster and for stars in the centre of Eridanus 2. We discuss the existence of the cluster and determine new constraints for MACHOs using the Fokker–Planck diffusion approximation. Results. Out of 182 extracted spectra, we identify 26 member stars of Eridanus 2, seven of which are possible cluster members. We find intrinsic mean line-of-sight velocities of 79.7+3.1−3.8 km s−1 and 76.0+3.2−3.7 km s−1 for the cluster and the bulk of Eridanus 2, respectively, as well as intrinsic velocity dispersions of < 7.6 km s−1 (68% upper limit) and 10.3+3.9−3.2 km s−1, respectively. This indicates that the cluster most likely exists as a distinct dynamical population hosted by Eridanus 2 and that it does not have a surplus of dark matter over the background distribution. Among the member stars in the bulk of Eridanus 2, we find possible carbon stars, alluding to the existence of an intermediate-age population. We derived constraints on the fraction of dark matter that can consist of MACHOs with a given mass between 1 and 105 M⊙. For dark matter consisting purely of MACHOs, the mass of the MACHOs must be less than ∼7.6 M⊙ and ∼44 M⊙ at a 68- and 95% confidence level, respectively.

scholarly journals Latest results on dark matter searches with H.E.S.S

2019 ◽  
Vol 209 ◽  
pp. 01023 ◽  
Author(s):  
Lucia Rinchiuso
Keyword(s):  
Dark Matter ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Mass Range ◽  
High Energy ◽  
Galactic Centre ◽  
Final States ◽  
Cherenkov Telescopes ◽  
Observation Strategy ◽  
Very High Energy

The nature of Dark Matter (DM) is one of the most debated questions of contemporary physics. Ground-based arrays of Cherenkov telescopes such as the High Energy Spectroscopic System (H.E.S.S.) search for DM signatures through the detection of Very-High-Energy (VHE, E > 100 GeV) gamma-rays. DM particles could selfannihilate in dense environments producing VHE γ-rays in the final states that could be eventually detected by H.E.S.S.. The H.E.S.S. observation strategy for DM search focuses towards the Galactic Centre (GC) region and nearby dwarf galaxy satellites of the Milky Way. The GC dataset provides the most stringent constraints on the DM annihilation cross section in the mass range 300 GeV - 70 TeV. Searches have been carried out towards classical and ultra-faint dwarf galaxies to test specific heavy DM models. The latest results towards the GC and dwarf galaxies are shown.

scholarly journals NIHAO – XXV. Convergence in the cusp-core transformation of cold dark matter haloes at high star formation thresholds

2020 ◽  
Vol 499 (2) ◽  
pp. 2648-2661
Author(s):  
Aaron A Dutton ◽  
Tobias Buck ◽  
Andrea V Macciò ◽  
Keri L Dixon ◽  
Marvin Blank ◽  
...  
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Good Description ◽  
Good Match ◽  
Virial Mass ◽  
Density Threshold

ABSTRACT We use cosmological hydrodynamical galaxy formation simulations from the NIHAO project to investigate the response of cold dark matter (CDM) haloes to baryonic processes. Previous work has shown that the halo response is primarily a function of the ratio between galaxy stellar mass and total virial mass, and the density threshold above which gas is eligible to form stars, n[cm−3]. At low n all simulations in the literature agree that dwarf galaxy haloes are cuspy, but at high n ≳ 100 there is no consensus. We trace halo contraction in dwarf galaxies with n ≳ 100 reported in some previous simulations to insufficient spatial resolution. Provided the adopted star formation threshold is appropriate for the resolution of the simulation, we show that the halo response is remarkably stable for n ≳ 5, up to the highest star formation threshold that we test, n = 500. This free parameter can be calibrated using the observed clustering of young stars. Simulations with low thresholds n ≤ 1 predict clustering that is too weak, while simulations with high star formation thresholds n ≳ 5, are consistent with the observed clustering. Finally, we test the CDM predictions against the circular velocities of nearby dwarf galaxies. Low thresholds predict velocities that are too high, while simulations with n ∼ 10 provide a good match to the observations. We thus conclude that the CDM model provides a good description of the structure of galaxies on kpc scales provided the effects of baryons are properly captured.

scholarly journals In Pursuit of the Least Luminous Galaxies

2010 ◽  
Vol 2010 ◽  
pp. 1-11 ◽  
Author(s):  
Beth Willman
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Field Survey ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Wide Field ◽  
Dark Matter Halos ◽  
The Past ◽  
Luminous Galaxies ◽  
Host Stars

The dwarf galaxy companions to the Milky Way are unique cosmological laboratories. With luminosities as low as10−7LMW, they inhabit the lowest mass dark matter halos known to host stars and are presently the most direct tracers of the distribution, mass spectrum, and clustering scale of dark matter. Their resolved stellar populations also facilitate detailed studies of their history and mass content. To fully exploit this potential requires a well-defined census of virtually invisible galaxies to the faintest possible limits and to the largest possible distances. I review the past and present impacts of survey astronomy on the census of Milky Way dwarf galaxy companions and discuss the future of finding ultra-faint dwarf galaxies around the Milky Way and beyond in wide-field survey data.

scholarly journals Chemo-dynamical evolution of dwarf galaxies: from flat to cuspy dark matter density profiles

2009 ◽  
Vol 5 (H15) ◽  
pp. 78-78
Author(s):  
S. Pasetto ◽  
E. K. Grebel ◽  
P. Berczik ◽  
R. Spurzem
Keyword(s):  
Dark Matter ◽  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Smooth Particle Hydrodynamic ◽  
Dynamical Evolution ◽  
Mass Range ◽  
Density Profiles ◽  
Hydrodynamic Approach ◽  
The Stability ◽  
Evolution With Time

A model of an isolated dwarf spherical galaxy (dSph) is considered in its chemo-dynamical evolution with time. The system is composed by 3 γ-model density profiles: gas, stellar and dark matter, and it is realized in a spherical symmetric equilibrium configuration. The total masses used in our simulations are covering the dwarf galaxies mass range. The stability of this configuration is first tested for the system evolving under the gravity effect alone and then evolved taking into account for the most relevant stellar astrophysical processes implemented with a Smooth Particle Hydrodynamic approach. The two different kinds of evolution are compared. The dark matter evolves naturally from a centrally cuspy density profile into a flatter one within a timescale of several Gyr. The effect manifests itself naturally, without any tuned initial conditions, as soon as few standard criteria on star formation are assumedand the SN feedback on the ISM has been adopted the prescription in (Cioffi & Shull 1991) and (Bradamante et al. 1998). This result is expected to be a possible natural explanation for the discrepancy between observations that want flatter dark matter profiles (e.g. de Block 2005), and N-body simulations that predict cuspy dark matter profiles (Navarro et al. 1997). Chemical considerations are presented as a tool to follow with observational parameters the theory predictions.

scholarly journals How the first stars shaped the faintest gas-dominated dwarf galaxies

2015 ◽  
Vol 11 (S317) ◽  
pp. 360-361
Author(s):  
Robbert Verbeke ◽  
Bert Vandenbroucke ◽  
Sven De Rijcke
Keyword(s):  
Dark Matter ◽  
Dwarf Galaxies ◽  
Ultra Violet ◽  
Mass Range ◽  
Dark Matter Halos ◽  
First Stars ◽  
Star Forming ◽  
Neutral Gas ◽  
Entire Mass Range ◽  
Fisher Relation

AbstractCosmological simulations predict that dark matter halos with circular velocities lower than 30 km/s should have lost most of their neutral gas by heating of the ultra-violet background. This is in stark contrast with gas-rich galaxies such as e.g. Leo T, Leo P and Pisces A, which all have circular velocities of ~15 km/s (Ryan-Weber et al. 2008, Bernstein-Cooper et al. 2014, Tollerud et al. 2015). We show that when we include feedback from the first stars into our models, simulated dwarfs have very different properties at redshift 0 than when this form of feedback is not included. Including this Population-III feedback leads to galaxies that lie on the baryonic Tully-Fisher relation over the entire mass range of star forming dwarf galaxies, as well as reproducing a broad range of other observational properties.

The inner structure of dark matter haloes in the Hubble sequence

2016 ◽  
Vol 25 (10) ◽  
pp. 1650093
Author(s):  
Antonino Del Popolo ◽  
Anna Saburova ◽  
Gaetano Belvedere
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Qualitative Agreement ◽  
Dwarf Galaxies ◽  
Rotation Velocity ◽  
Mass Range ◽  
Density Profiles ◽  
Hubble Sequence ◽  
Stellar Masses ◽  
Morphology Changes

We study how galaxy morphology changes the relation among the inner slope [Formula: see text] of galactic density profiles and the stellar mass, and rotation velocity. We find that the slope [Formula: see text] flattens monotonically from [Formula: see text] to [Formula: see text] going from giant galaxies (ellipticals, spirals) to dwarf galaxies ([Formula: see text]). At masses smaller than [Formula: see text], in the mass range dominated by nonrotational supported galaxies (e.g. dSphs), the slope steepens due to the offset in angular momentum of rotational dominated, and nonrotational dominated galaxies. A comparison with SPH simulations finds our result in qualitative agreement with them, but the inner slope [Formula: see text] at small stellar masses is flatter than that in their simulations. Density profiles become cuspy for [Formula: see text] in the range [Formula: see text]–[Formula: see text], similarly to Õnorbe.

scholarly journals Accurate mass estimates from the proper motions of dispersion-supported galaxies

2020 ◽  
Vol 493 (4) ◽  
pp. 5825-5837 ◽  
Author(s):  
Alexandres Lazar ◽  
James S Bullock
Keyword(s):  
Dark Matter ◽  
Proper Motion ◽  
Cold Dark Matter ◽  
Dwarf Galaxy ◽  
Tangential Velocity ◽  
Line Of Sight ◽  
Proper Motions ◽  
Characteristic Radius ◽  
Motion Measurements ◽  
Rule Out

ABSTRACT We derive a new mass estimator that relies on internal proper motion measurements of dispersion-supported stellar systems, one that is distinct and complementary to existing estimators for line-of-sight velocities. Starting with the spherical Jeans equation, we show that there exists a radius where the mass enclosed depends only on the projected tangential velocity dispersion, assuming that the anisotropy profile slowly varies. This is well-approximated at the radius where the log-slope of the stellar tracer profile is −2: r−2. The associated mass is $M(r_{-2}) = 2 G^{-1} \langle \sigma _{\mathcal {T}}^{2}\rangle ^{*} r_{-2}$ and the circular velocity is $V^{2}({r_{-2}}) = 2\langle \sigma _{\mathcal {T}}^{2}\rangle ^{*}$. For a Plummer profile r−2 ≃ 4Re/5. Importantly, r−2 is smaller than the characteristic radius for line-of-sight velocities derived by Wolf et al. Together, the two estimators can constrain the mass profiles of dispersion-supported galaxies. We illustrate its applicability using published proper motion measurements of dwarf galaxies Draco and Sculptor, and find that they are consistent with inhabiting cuspy NFW subhaloes of the kind predicted in CDM but we cannot rule out a core. We test our combined mass estimators against previously published, non-spherical cosmological dwarf galaxy simulations done in both cold dark matter (CDM; naturally cuspy profile) and self-interacting dark matter (SIDM; cored profile). For CDM, the estimates for the dynamic rotation curves are found to be accurate to $10\rm { per\, cent}$ while SIDM are accurate to $15\rm { per\, cent}$. Unfortunately, this level of accuracy is not good enough to measure slopes at the level required to distinguish between cusps and cores of the type predicted in viable SIDM models without stronger priors. However, we find that this provides good enough accuracy to distinguish between the normalization differences predicted at small radii (r ≃ r−2 &lt; rcore) for interesting SIDM models. As the number of galaxies with internal proper motions increases, mass estimators of this kind will enable valuable constraints on SIDM and CDM models.

scholarly journals Influence of the Void Environment on Chemical Abundances in Dwarf Galaxies and Implications for Connecting Star Formation and Halo Mass

2018 ◽  
Vol 14 (S344) ◽  
pp. 369-372
Author(s):  
Kelly A. Douglass ◽  
Michael S. Vogeley ◽  
Renyue Cen
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Large Scale ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Direct Method ◽  
Dark Matter Halo ◽  
Chemical Abundances ◽  
Abundance Estimates ◽  
Galaxy Populations

AbstractWe study how the void environment affects the chemical evolution of galaxies by comparing the metallicity of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from SDSS DR7, we estimate oxygen and nitrogen abundances of 889 void dwarf galaxies and 672 dwarf galaxies in denser regions. A substitute for the [OII] λ3727 doublet is developed, permitting oxygen abundance estimates of SDSS dwarf galaxies at all redshifts with the direct method. We find that void dwarf galaxies have about the same oxygen abundances and slightly lower N/O ratios than dwarf galaxies in denser environments. The lower N/O ratios seen in void dwarf galaxies may indicate both delayed star formation and a dependence of cosmic downsizing on the large-scale environment. Similar oxygen abundances in the two dwarf galaxy populations might be evidence of larger ratios of dark matter halo mass to stellar mass in voids.

scholarly journals Ghostly haloes in dwarf galaxies: constraints on the star formation efficiency before reionization

2019 ◽  
Vol 488 (2) ◽  
pp. 2673-2688
Author(s):  
Hoyoung D Kang ◽  
Massimo Ricotti
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Dwarf Galaxies ◽  
Mass Range ◽  
Small Mass ◽  
Dark Matter Halo ◽  
Host Galaxy ◽  
Normal Galaxies ◽  
Stellar Halo ◽  
Formation Efficiency

ABSTRACT Stellar haloes observed around normal galaxies are extended and faint stellar structures formed by debris of tidally disrupted dwarf galaxies accreted overtime by the host galaxy. Around dwarf galaxies, these stellar haloes may not exist if all the accreted satellites are dark haloes without stars. However, if a stellar halo is found in sufficiently small mass dwarfs, the whole stellar halo is composed of tidal debris of fossil galaxies, and we refer to it as ghostly halo. Fossil galaxies are so called because they formed most of their stars before the epoch of reionization, and have been identified as the ultrafaint dwarf galaxies found around the Milky Way and M31. In this paper, we carry out semi-analytical simulations to characterize the sizes and stellar masses of ghostly stellar haloes in dwarf galaxies as a function of their dark matter halo mass. By comparing the models to observations of six isolated dwarf galaxies in the Local Group showing evidence of extended stellar haloes, we are able to constrain the star formation efficiency in fossil galaxies. We find that at redshift z ∼ 6, dark matter haloes in the mass range 107–109 M⊙ have a mean star formation efficiency $f_* \equiv M_*/M_{\mathrm{ dm}} \sim 0.1\!-\!0.2\hbox{ per cent}$ nearly constant as a function of the dark matter halo mass.

scholarly journals The Faint Globular Cluster in the Dwarf Galaxy Andromeda I

2017 ◽  
Vol 34 ◽  
Author(s):  
Nelson Caldwell ◽  
Jay Strader ◽  
David J. Sand ◽  
Beth Willman ◽  
Anil C. Seth
Keyword(s):  
Dark Matter ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Dark Matter Halos ◽  
History Of ◽  
Low Mass ◽  
Growing Population

AbstractObservations of globular clusters in dwarf galaxies can be used to study a variety of topics, including the structure of dark matter halos and the history of vigorous star formation in low-mass galaxies. We report on the properties of the faint globular cluster (MV ~ −3.4) in the M31 dwarf galaxy Andromeda I. This object adds to the growing population of low-luminosity Local Group galaxies that host single globular clusters.

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