The abundance of dwarf galaxies around low-mass giants in the Local Volume
TL;DR: In this paper, the authors used the Dark Energy Camera (DEC) to search for previously undetected dwarf galaxies in the Sculptor group of the Local Volume galaxies (LVGs).
Abstract: The abundance of satellite dwarf galaxies has long been considered a crucial test for the current model of cosmology leading to the well-known missing satellite problem Recent advances in both simulations and observations have allowed to study dwarf galaxies around host galaxies in more detail We have surveyed a 72 deg2 area of the nearby Sculptor group using the Dark Energy Camera - also encompassing the two low-mass Local Volume galaxies NGC24 and NGC45 residing behind the group - to search for hitherto undetected dwarf galaxies Apart from the previously known dwarf galaxies we have found only two new candidates down to a 3 sigma surface brightness detection limit of 274 r mag arcsec-2 Both systems are in projection close to NGC24 However, one of these candidates could be an ultra-diffuse galaxy associated to a background galaxy We compared the number of known dwarf galaxy candidates around NGC24, NGC45, and five other well-studied low-mass giant galaxies (NGC 1156, NGC2403, NGC5023, M33, and the LMC) with predictions from cosmological simulations and found that for the stellar-to-halo mass models considered, the observed satellite numbers tend to be on the lower end of the expected range This could either mean that there is an over-prediction of luminous subhalos in LambdaCDM or - and more likely - that we are missing some of the satellite members due to observational biases
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TL;DR: In this article , the authors consider the most notable challenges to the dark energy plus cold dark matter (ΛCDM) cosmological model regarding dwarf galaxies and discuss how recent cosmologically numerical simulations have pinpointed baryonic solutions to these challenges.
Abstract: Galaxies and their dark-matter haloes have posed several challenges to the dark energy plus cold dark matter (ΛCDM) cosmological model. These discrepancies between observations and theory intensify for the lowest-mass (‘dwarf’) galaxies. ΛCDM predictions for the number, spatial distribution and internal structure of low-mass dark-matter haloes have historically been at odds with observed dwarf galaxies, but this is partially expected, because many predictions modelled only the dark-matter component. Any robust ΛCDM prediction must include, hand in hand, a model for galaxy formation to understand how baryonic matter populates and affects dark-matter haloes. In this Review, we consider the most notable challenges to ΛCDM regarding dwarf galaxies, and we discuss how recent cosmological numerical simulations have pinpointed baryonic solutions to these challenges. We identify remaining tensions, including the diversity of the inner dark-matter content, planes of satellites, stellar morphologies and star-formation quenching. Their resolution, or validation as actual problems with ΛCDM, will probably require both refining of galaxy-formation models and improving numerical accuracy in simulations. Galaxies and their dark-matter haloes have posed several challenges to the dark energy plus cold dark matter (ΛCDM) cosmological model. This Review discusses the most notable challenges to ΛCDM regarding dwarf galaxies and the insights provided by recent cosmological numerical simulations.
31 citations
TL;DR: The final sample of the Exploration of Local VolumE Satellites (ELVES) survey as mentioned in this paper is a survey of the dwarf satellites of a nearly volume-limited sample of Milky Way (MW)−like hosts in the Local Volume.
Abstract: We present the final sample of the Exploration of Local VolumE Satellites (ELVES) survey, a survey of the dwarf satellites of a nearly volume-limited sample of Milky Way (MW)−like hosts in the Local Volume. Hosts are selected simply via a cut in luminosity ( MKs<−22.1 mag) and distance (D < 12 Mpc). We cataloged the satellites of 25 of the 31 such hosts, with another five taken from the literature. All hosts are surveyed out to at least 150 projected kpc ( ∼ R vir/2), with the majority surveyed to 300 kpc ( ∼ R vir). Satellites are detected using a consistent semiautomated algorithm specialized for low surface brightness dwarfs. As shown through extensive tests with injected galaxies, the catalogs are complete to M V ∼ −9 mag and μ 0,V ∼ 26.5 mag arcsec−2. Candidates are confirmed to be real satellites through distance measurements including redshift, tip of the red giant branch, and surface brightness fluctuations. Across all 30 surveyed hosts, there are 338 confirmed satellites with M V < −9 mag, with a further 106 candidates awaiting distance measurement. For the vast majority of these, we provide consistent multiband Sérsic photometry. We show that satellite abundance correlates with host mass, with the MW being quite typical among comparable systems, and that satellite quenched fraction rises steeply with decreasing satellite mass, mirroring the quenched fraction for the MW and M31. The ELVES survey represents a massive increase in the statistics of surveyed systems with known completeness, and the provided catalogs are a unique data set to explore various aspects of small-scale structure and dwarf galaxy evolution.
21 citations
TL;DR: In this article, the authors present results from a resolved stellar population search for dwarf satellite galaxies of six nearby (D < 5$ Mpc), sub-Milky-Way mass hosts using deep optical imaging from the Large Binocular Telescope.
Abstract: We present results from a resolved stellar population search for dwarf satellite galaxies of six nearby (D $<5$ Mpc), sub-Milky-Way mass hosts using deep ($m\sim27$ mag) optical imaging from the Large Binocular Telescope. We perform image simulations to quantify our detection efficiency for dwarfs over a large range in luminosity and size, and develop a fast catalog-based emulator that includes a treatment of unresolved photometric blending. We discover no new dwarf satellites, but we recover two previously known dwarfs (DDO 113 and LV J1228+4358) with $M_{\text{V}}<-12$ that lie in our survey volume. We preview a new theoretical framework to predict satellite luminosity functions using analytic probability distribution functions and apply it to our sample, finding that we predict one fewer classical dwarf and one more faint dwarf ($M_{\text{V}}\sim-7.5$) than we find in our observational sample (i.e., the observational sample is slightly top-heavy). However, the overall number of dwarfs in the observational sample (2) is in good agreement with the theoretical expectations. Interestingly, DDO 113 shows signs of environmental quenching and LV J1228+4358 is tidally disrupting, suggesting that low-mass hosts may affect their satellites more severely than previously believed.
8 citations
TL;DR: In this paper, the authors derived a halo mass of luminous galaxies via orbital motion of their companions, which was then used to derive the average total mass-to-K$-band luminosity ratio.
Abstract: Rapid advance has been made recently in accurate distance measurements for nearby ($D < 11$ Mpc) galaxies based on the magnitude of the tip of red giant branch stars resolved with the Hubble Space Telescope. We use observational properties of galaxies presented in the last version of Updated Nearby Galaxy Catalog to derive a halo mass of luminous galaxies via orbital motion of their companions. Our sample contains 298 assumed satellites with known radial velocities around 25 Milky Way-like massive galaxies and 65 assumed satellites around 47 fainter dominant galaxies. The average total mass-to-$K$-band luminosity ratio is $31\pm6 M_\odot/L_\odot$ for the luminous galaxies, increasing up to $\sim200 M_\odot/L_\odot$ toward dwarfs. The bulge-dominated luminous galaxies are characterized with $\langle{}M_T/L_K\rangle = 73\pm15 M_\odot/L_\odot$, while the disc-dominated spirals have $\langle{}M_T/L_K\rangle = 17.4\pm2.8 M_\odot/L_\odot$. We draw attention to a particular subsample of luminous spiral galaxies with signs of declining rotation curve, which have a radial velocity dispersion of satellites less than 55 km/s and a poor dark matter halo with $\langle{}M_T/L_K\rangle = 5.5\pm1.1 M_\odot/L_\odot$. We note that a fraction of quenched (dSph, dE) companions around Milky Way-like galaxies decreases with their linear projected separation as $0.75 \exp(-R_p/350\,\mathrm{kpc})$.
7 citations
TL;DR: In this article, the authors analyzed the 2D spatial distribution of 2210 dwarf galaxies around early-type galaxies (ETGs) in the low-to-medium density fields of the "Mass Assembly of early-Type GaLAxies with their fine Structures" (MATLAS) survey.
Abstract: It was first observed in the 1970s that the dwarf galaxies surrounding our Milky Way, so-called satellites, appear to be arranged in a thin, vast plane. Similar discoveries have been made around additional galaxies in the local Universe such as Andromeda, Centaurus A, and potentially M83. In the specific cases with available kinematic data, the dwarf satellites also appear to preferentially co-orbit their massive host galaxy. Planes of satellites are rare in the lambda cold dark matter ($\Lambda$CDM) paradigm, although they may be a natural consequence of projection effects. Such a phase-space correlation, however, remains difficult to explain. In this work we analyzed the 2D spatial distribution of 2210 dwarf galaxies around early-type galaxies (ETGs) in the low-to-medium density fields of the "Mass Assembly of early-Type GaLAxies with their fine Structures" (MATLAS) survey. Under the assumption that the dwarfs are satellite members of the central massive ETG, we identified flattened structures using both a variation in the Hough transform and total least square (TLS) fitting. In 119 satellite systems, we find 31 statistically significant flattened dwarf structures using a combination of both methods with subsequent Monte Carlo (MC) simulations with random data. The vast majority of these dwarf structures lie within the estimated virial radii of the massive host. The major axes of these systems are aligned better than 30° with the estimated orientation of the large-scale structure in nine (50%) cases. Additional distance measurements and future kinematic studies will be required to confirm the planar nature of these structures and to determine if they are corotating systems.
6 citations
References
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TL;DR: The SExtractor ( Source Extractor) as mentioned in this paper is an automated software that optimally detects, deblends, measures and classifies sources from astronomical images, which is particularly suited to the analysis of large extragalactic surveys.
Abstract: We present the automated techniques we have developed for new software that optimally detects, deblends, measures and classifies sources from astronomical images: SExtractor ( Source Extractor ). We show that a very reliable star/galaxy separation can be achieved on most images using a neural network trained with simulated images. Salient features of SExtractor include its ability to work on very large images, with minimal human intervention, and to deal with a wide variety of object shapes and magnitudes. It is therefore particularly suited to the analysis of large extragalactic surveys.
10,983 citations
TL;DR: In this article, the substructure clumps are on orbits that take a large fraction of them through the stellar disk, leading to significant resonant and impulsive heating, and the model predicts that the virialized extent of the Milky Way's halo should contain about 500 satellites with circular velocities larger than the Draco and Ursa Minor systems, i.e., bound masses 108 M☉ and tidally limited sizes 1 kpc.
Abstract: We use numerical simulations to examine the substructure within galactic and cluster mass halos that form within a hierarchical universe. Clusters are easily reproduced with a steep mass spectrum of thousands of substructure clumps that closely matches the observations. However, the survival of dark matter substructure also occurs on galactic scales, leading to the remarkable result that galaxy halos appear as scaled versions of galaxy clusters. The model predicts that the virialized extent of the Milky Way's halo should contain about 500 satellites with circular velocities larger than the Draco and Ursa Minor systems, i.e., bound masses 108 M☉ and tidally limited sizes 1 kpc. The substructure clumps are on orbits that take a large fraction of them through the stellar disk, leading to significant resonant and impulsive heating. Their abundance and singular density profiles have important implications for the existence of old thin disks, cold stellar streams, gravitational lensing, and indirect/direct detection experiments.
3,037 citations
TL;DR: GALFIT as mentioned in this paper is a two-dimensional fitting algorithm designed to extract structural components from galaxy images, with emphasis on closely modeling light profiles of spatially well-resolved, nearby galaxies observed with the Hubble Space Telescope.
Abstract: We present a two-dimensional fitting algorithm (GALFIT) designed to extract structural components from galaxy images, with emphasis on closely modeling light profiles of spatially well-resolved, nearby galaxies observed with the Hubble Space Telescope. Our algorithm improves on previous techniques in two areas: by being able to simultaneously fit a galaxy with an arbitrary number of components and with optimization in computation speed, suited for working on large galaxy images. We use two-dimensional models such as the "Nuker" law, the Sersic (de Vaucouleurs) profile, an exponential disk, and Gaussian or Moffat functions. The azimuthal shapes are generalized ellipses that can fit disky and boxy components. Some potential applications of our program include: standard modeling of global galaxy profiles; extracting bars, stellar disks, double nuclei, and compact nuclear sources; and measuring absolute dust extinction or surface brightness fluctuations after removing the galaxy model. When examined in detail, we find that even simple looking galaxies generally require at least three components to be modeled accurately, rather than the one or two components more often employed. Many galaxies with complex isophotes, ellipticity changes, and position angle twists can be modeled accurately in two dimensions. We illustrate this by way of 11 case studies, which include regular and barred spiral galaxies, highly disky lenticular galaxies, and elliptical galaxies displaying various levels of complexities. A useful extension of this algorithm is to accurately extract nuclear point sources in galaxies. We compare two-dimensional and one-dimensional extraction techniques on simulated images of galaxies having nuclear slopes with different degrees of cuspiness, and we then illustrate the application of the program to several examples of nearby galaxies with weak nuclei.
2,670 citations
TL;DR: In this paper, the substructure clumps are on orbits that take a large fraction of them through the stellar disk leading to significant resonant and impulsive heating, and the model predicts that the virialised extent of the Milky Way's halo should contain about 500 satellites with circular velocities larger than Draco and Ursa-Minor i.e. bound masses > 10^8Mo and tidally limited sizes > kpc.
Abstract: We use numerical simulations to examine the substructure within galactic and cluster mass halos that form within a hierarchical universe. Clusters are easily reproduced with a steep mass spectrum of thousands of substructure clumps that closely matches observations. However, the survival of dark matter substructure also occurs on galactic scales, leading to the remarkable result that galaxy halos appear as scaled versions of galaxy clusters. The model predicts that the virialised extent of the Milky Way's halo should contain about 500 satellites with circular velocities larger than Draco and Ursa-Minor i.e. bound masses > 10^8Mo and tidally limited sizes > kpc. The substructure clumps are on orbits that take a large fraction of them through the stellar disk leading to significant resonant and impulsive heating. Their abundance and singular density profiles has important implications for the existence of old thin disks, cold stellar streams, gravitational lensing and indirect/direct detection experiments.
2,595 citations
TL;DR: In this paper, dissipationless CDM simulations predict that the majority of themost massive subhalos of the Milky Way are too dense to host any of its brightsatellites (L V > 10 5 L ).
Abstract: We show that dissipationless CDM simulations predict that the majority of themost massive subhalos of the Milky Way are too dense to host any of its brightsatellites (L V > 10 5 L ). These dark subhalos have circular velocities at infall ofV infall = 30 1070kms 1 and infall masses of [0:2 4] 10 M . Unless the Milky Way isa statistical anomaly, this implies that galaxy formation becomes e ectively stochasticat these masses. This is in marked contrast to the well-established monotonic relationbetween galaxy luminosity and halo circular velocity (or halo mass) for more massivehalos. We show that at least two (and typically four) of these massive dark subhalosare expected to produce a larger dark matter annihilation ux than Draco. It maybe possible to circumvent these conclusions if baryonic feedback in dwarf satellites ordi erent dark matter physics can reduce the central densities of massive subhalos byorder unity on a scale of 0.3 { 1 kpc.Key words: Galaxy: halo { galaxies: abundances { dark matter { cosmology: theory
1,280 citations