Galaxies are generally found to follow a relation between their size and luminosity, such that luminous galaxies typically have large sizes. The recent identification of a significant population of ...galaxies with large sizes but low luminosities ("ultra diffuse galaxies," or UDGs) raises the question of whether the inverse is also true-that is, whether large galaxies typically have high luminosities. Here we address this question by studying a size-limited sample of galaxies in the Coma cluster. We select red cluster galaxies with sizes of reff > 2 kpc down to Mg ∼ −13 mag in an area of 9 deg2, using carefully filtered Canada-France-Hawaii Telescope images. The sample is complete to a central surface brightness of g,0 25.0 mag arcsec−2 and includes 90% of Dragonfly-discovered UDGs brighter than this limit. Unexpectedly, we find that red, large galaxies have a fairly uniform distribution in the size-luminosity plane: there is no peak at the absolute magnitude implied by the canonical size-luminosity relation. The number of galaxies within 0.5 mag of the canonical peak (Mg = −19.69 for 2 < reff < 3 kpc) is a factor of ∼9 smaller than the number of fainter galaxies with −19 < Mg < −13. Large, faint galaxies, such as UDGs, are far more common than large galaxies that are on the size-luminosity relation. An implication is that, for large galaxies, size is not an indicator of the halo mass. Finally, we show that the structure of faint large galaxies is different from that of bright large galaxies: at a fixed large size, the Sérsic index decreases with the magnitude following the relation .
We discuss the approach of searching the lowest mass dwarf galaxies, , in the general field, using integrated light surveys. By exploring the limiting surface brightness-spatial resolution ( ...eff,lim−θ) parameter space, we suggest that faint field dwarfs in the Local Volume, between 3 and 10 Mpc, are expected to be detected very effectively and in large numbers using integrated light photometric surveys, complementary to the classical star counts method. We use a sample of dwarf galaxies in the Local Group to construct relations between their photometric and structural parameters, M*- eff,V and M*-Reff. We use these relations, along with assumed functional forms for the halo mass function and the stellar mass-halo mass (SMHM) relation, to calculate the lowest detectable stellar masses in the Local Volume and the expected number of galaxies as a function of the limiting surface brightness and spatial resolution. The number of detected galaxies depends mostly on the limiting surface brightness for distances >3 Mpc, while spatial resolution starts to play a role for galaxies at distances >8 Mpc. Surveys with eff,lim ∼ 30 mag arcsec−2 should be able to detect galaxies with stellar masses down to ∼104 M in the Local Volume. Depending on the form of the SMHM relation, the expected number of dwarf galaxies with distances between 3 and 10 Mpc is 0.04-0.35 per square degree, assuming a limiting surface brightness of ∼29-30 mag arcsec−2 and a spatial resolution <4″. We plan to search for a population of low-mass dwarf galaxies in the field by performing a blank wide field photometric survey with the Dragonfly Telephoto Array, an imaging system optimized for the detection of extended ultra low surface brightness structures.
The ultra-diffuse galaxy NGC1052-DF2 has a very low velocity dispersion, indicating that it has little or no dark matter. Here we report the discovery of a second galaxy in this class, residing in ...the same group. NGC1052-DF4 closely resembles NGC1052-DF2 in terms of its size, surface brightness, and morphology; has a similar distance of ; and also has a population of luminous globular clusters extending out to from the center of the galaxy. Accurate radial velocities of the diffuse galaxy light and seven of the globular clusters were obtained with the Low Resolution Imaging Spectrograph on the Keck I telescope. The velocity of the diffuse light is identical to the median velocity of the clusters, , and close to the central velocity of the NGC 1052 group. The rms spread of the globular cluster velocities is very small at . Taking observational uncertainties into account we determine an intrinsic velocity dispersion of , consistent with the expected value from the stars alone ( ) and lower than expected from a standard NFW halo ( ). We conclude that NGC1052-DF2 is not an isolated case but that a class of such objects exists. The origin of these large, faint galaxies with an excess of luminous globular clusters and an apparent lack of dark matter is, at present, not understood.
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 (
M
K
s
<
−
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.
Abstract
We present
Art
ificial Stellar
Pop
ulations (
ArtPop
), an open-source Python package for synthesizing stellar populations and generating artificial images of stellar systems, populated star ...by star. The code is designed to be intuitive to use and as modular as possible, making it possible to use each of its functionalities independently or together.
ArtPop
has a wide range of scientific and pedagogical use cases, including the measurement of detection efficiencies in current and future imaging surveys, the calculation of integrated stellar population parameters, quantitative comparisons of isochrone models, and the development and validation of astronomical image-processing algorithms. In this paper, we give an overview of the
ArtPop
package, provide simple coding examples to demonstrate its implementation, and present results from some potential applications of the code. We provide links to the source code that created each example and figure throughout the paper.
ArtPop
is under active development, and we welcome bug reports, feature requests, and code contributions from the community.
https://artpop.readthedocs.io/en/latest/
https://github.com/ArtificialStellarPopulations/ArtPop/
https://artpop.readthedocs.io/en/latest/tutorials/quickstart.html
https://github.com/ArtificialStellarPopulations/artpop-paper-figures/blob/main/scripts/
Abstract
NGC 1052-DF2 and NGC 1052-DF4 are ultradiffuse galaxies that have extremely low velocity dispersions, indicating that they have little or no dark matter. Both galaxies host anomalously ...luminous globular clusters (GCs), with a peak magnitude of their GC luminosity function (GCLF) that is ∼1.5 mag brighter than the near-universal value of
M
V
≈ −7.5. Here we present an analysis of the joint GCLF of the two galaxies, making use of new Hubble Space Telescope photometry and Keck spectroscopy and a recently improved distance measurement. We apply a homogeneous photometric selection method to the combined GC sample of DF2 and DF4. The new analysis shows that the peak of the combined GCLF remains at
M
V
≈ −9 mag. In addition, we find a subpopulation of less luminous GCs at
M
V
≈ −7.5 mag, where the near-universal GCLF peak is located. The number of GCs in the magnitude range of −5 to −8 is
in DF2 and
in DF4, similar to that expected from other galaxies of the same luminosity. The total GC number between
M
V
of −5 and −11 is
for DF2 and
for DF4, calculated from the background-subtracted GCLF. The data are consistent with both galaxies having two GC populations: the one expected for their luminosity, and a very luminous population composing ∼90% of the total cluster mass. The number of GCs does not scale with the halo mass in either DF2 or DF4, suggesting that
N
GC
is not directly determined by the merging of halos.
The velocity dispersion of the ultra diffuse galaxy NGC1052-DF2 was found to be km s−1, much lower than expected from the stellar mass-halo mass relation and nearly identical to the expected value ...from the stellar mass alone. This result was based on the radial velocities of 10 luminous globular clusters that were assumed to be associated with the galaxy. A more precise measurement is possible from high-resolution spectroscopy of the diffuse stellar light. Here we present an integrated spectrum of the diffuse light of NGC1052-DF2 obtained with the Keck Cosmic Web Imager (KCWI), with an instrumental resolution of instr 12 km s−1. The systemic velocity of the galaxy is vsys = 1805 1.1 km s−1, in very good agreement with the average velocity of the globular clusters ( km s−1). There is no evidence for rotation within the KCWI field of view. We find a stellar velocity dispersion of km s−1, consistent with the dispersion that was derived from the globular clusters. The implied dynamical mass within the half-light radius r1/2 = 2.7 kpc is Mdyn = (1.3 0.8) × 108 M , similar to the stellar mass within that radius (Mstars = (1.0 0.2) × 108 M ). With this confirmation of the low velocity dispersion of NGC1052-DF2, the most urgent question is whether this "missing dark matter problem" is unique to this galaxy or applies more widely.
We present spatially resolved stellar kinematics of the well-studied ultra-diffuse galaxy (UDG) Dragonfly 44, as determined from 25.3 hr of observations with the Keck Cosmic Web Imager. The ...luminosity-weighted dispersion within the half-light radius is km s−1, lower than what we had inferred before from a DEIMOS spectrum in the H region. There is no evidence for rotation, with (90% confidence) along the major axis, in possible conflict with models where UDGs are the high-spin tail of the normal dwarf galaxy distribution. The spatially averaged line profile is more peaked than a Gaussian, with Gauss-Hermite coefficient h4 = 0.13 0.05. The mass-to-light ratio (M/L) within the effective radius is M /L , similar to other UDGs and higher by a factor of six than smaller galaxies of the same luminosity. This difference between UDGs and other galaxies is, however, sensitive to the aperture that is used, and it is much reduced when the M/L ratios are measured within a fixed radius of 10 kpc. Dragonfly 44 has a rising velocity dispersion profile, from km s−1 at R = 0.2 kpc to km s−1 at R = 5.1 kpc. The profile can only be fit with a cuspy Navarro-Frenk-White profile if the orbital distribution has strong tangential anisotropy, with . An alternative explanation is that the dark matter profile has a core: a Di Cintio et al. density profile with a mass-dependent core provides a very good fit to the kinematics for a halo mass of and , i.e., isotropic orbits. This model predicts a slight positive kurtosis, in qualitative agreement with the measured h4 parameter. UDGs such as Dragonfly 44 are dark matter dominated even in their centers and can constrain the properties of dark matter in a regime where baryons usually dominate the kinematics: small spatial scales in massive halos. In a companion paper we provide constraints on the axion mass in the context of "fuzzy" dark matter models.
We recently inferred that the galaxy NGC 1052-DF2 has little or no dark matter and a rich system of unusual globular clusters. We assumed that the galaxy is a satellite of the luminous elliptical ...galaxy NGC 1052 at 20 Mpc, on the basis of its surface brightness fluctuations (SBFs) distance of 19.0 1.7 Mpc, its radial velocity of 1800 km s−1, and its projected position. Here we analyze the color-magnitude diagram (CMD) of NGC 1052-DF2, following the suggestion by Trujillo et al. that the tip of the red giant branch (TRGB) can be detected in currently available Hubble Space Telescope (HST) data and the galaxy is at ∼13 Mpc. Using fully populated galaxy models we show that the CMD is strongly influenced by blends. These blends produce a "phantom" TRGB ∼2 times brighter than the true TRGB, which can lead to erroneous distance estimates ∼1.4 times smaller than the actual distance. We compare NGC 1052-DF2 to model images as well as other galaxies in our HST sample, and show that the large population of unblended RGB stars expected for distances of ∼13 Mpc is not detected. We also provide a new distance measurement to NGC 1052-DF2 that is free of calibration uncertainties, by anchoring it to a satellite of the megamaser host galaxy NGC 4258. From a megamaser-TRGB-SBF distance ladder we obtain D = 18.7 1.7 Mpc, consistent with our previous measurement and with the distance to the elliptical galaxy NGC 1052.
Abstract
Ultra-diffuse galaxies that contain a large sample of globular clusters (GCs) offer an opportunity to test the predictions of galactic dynamics theory. NGC5846-UDG1 is an excellent example, ...with a high-quality sample of dozens of GC candidates. We show that the observed distribution of GCs in NGC5846-UDG1 is suggestive of mass segregation induced by gravitational dynamical friction. We present simple analytic calculations, backed by a series of numerical simulations, that naturally explain the observed present-day pattern of GC masses and radial positions. Subject to some assumptions on the GC population at birth, the analysis supports the possibility that NGC5846-UDG1 resides in a massive dark matter halo. This is an example for the use of GC-rich systems as dynamical (in addition to kinematical) tracers of dark matter.
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