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Register a new userStructure and morphology of the MATLAS dwarf galaxies and their central nuclei
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We present a photometric study of the dwarf galaxy population in the low to moderate density environments of the MATLAS (Mass Assembly of early-Type gaLAxies with their fine Structures) deep imaging survey. The sample consists of 2210 dwarfs, including 508 nucleated. We define a nucleus as a compact source that is close to the galaxy photocentre (within 0.5 $R_e$) which is also the brightest such source within the galaxys effective radius. The morphological analysis is performed using a 2D surface brightness profile modelling on the g-band images of both the galaxies and nuclei. Our study reveals that, for similar luminosities, the MATLAS dwarfs show ranges in the distribution of structural properties comparable to cluster (Virgo and Fornax) dwarfs and a range of sizes comparable to the Local Group and Local Volume dwarfs. Colour measurements using the r- and i-band images indicate that the dwarfs in low and moderate density environments are as red as cluster dwarfs on average. The observed similarities between dwarf ellipticals in vastly different environments imply that dEs are not uniquely the product of morphological transformation due to ram-pressure stripping and galaxy harassment in high density environments. We measure that the dwarf nuclei are located predominantly in massive, bright and round dwarfs and observe fewer nuclei in dwarfs with a faint centre and a small size. The colour of the galaxy nucleus shows no clear relation to the colour of the dwarf, in agreement with the migration and wet migration nucleus formation scenarios. The catalogues of the MATLAS dwarfs photometric and structural properties are provided.
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We present the photometric properties of 2210 newly identified dwarf galaxy candidates in the MATLAS fields. The Mass Assembly of early Type gaLAxies with their fine Structures (MATLAS) deep imaging survey mapped $sim$142 deg$^2$ of the sky around nearby isolated early type galaxies using MegaCam on the Canada-France-Hawaii Telescope, reaching surface brightnesses of $sim$ 28.5 - 29 in the g-band. The dwarf candidates were identified through a direct visual inspection of the images and by visually cleaning a sample selected using a partially automated approach, and were morphologically classified at the time of identification. Approximately 75% of our candidates are dEs, indicating that a large number of early type dwarfs also populate low density environments, and 23.2% are nucleated. Distances were determined for 13.5% of our sample using pre-existing $z_{spec}$ measurements and HI detections. We confirm the dwarf nature for 99% of this sub-sample based on a magnitude cut $M_g$ = -18. Additionally, most of these ($sim$90%) have relative velocities suggesting that they form a satellite population around nearby massive galaxies rather than an isolated field sample. Assuming that the candidates over the whole survey are satellites of the nearby galaxies, we demonstrate that the MATLAS dwarfs follow the same scaling relations as dwarfs in the Local Group as well as the Virgo and Fornax clusters. We also find that the nucleated fraction increases with $M_g$, and find evidence of a morphology-density relation for dwarfs around isolated massive galaxies.
We present the analysis of medium-resolution spectra obtained at the Southern African Large Telescope (SALT) for nuclear globular clusters (GCs) in two dwarf spheroidal galaxies (dSphs). The galaxies have similar star formation histories, but they are situated in completely different environments. ESO269-66 is a close neighbour of the giant S0 NGC5128. KKs3 is one of the few truly isolated dSphs within 10 Mpc. We estimate the helium abundance $Y=0.3$, $rm age=12.6pm1$ Gyr, $[Fe/H]=-1.5,-1.55pm0.2$ dex, and abundances of C, N, Mg, Ca, Ti, and Cr for the nuclei of ESO269-66 and KKs3. Our surface photometry results using HST images yield the half-light radius of the cluster in KKs3, $rm r_h=4.8pm0.2$ pc. We demonstrate the similarities of medium-resolution spectra, ages, chemical compositions, and structure for GCs in ESO269-66 and KKs3 and for several massive Galactic GCs with $[Fe/H]sim-1.6$ dex. All Galactic GCs posses Extended Blue Horizontal Branches and multiple stellar populations. Five of the selected Galactic objects are iron-complex GCs. Our results indicate that the sample GCs observed now in different environments had similar conditions of their formation $sim$1 Gyr after the Big Bang.
Ultra-diffuse galaxies (UDGs) are very low-surface brightness galaxies with large effective radii. Spectroscopic measurements of a few UDGs have revealed a low dark matter content, based on the internal motion of stars or globular clusters (GCs). This is in contrast to the large number of GCs found for these systems, from which it would be expected to correspond to a large dark matter halo mass. Here we present Hubble Space Telescope Advanced Camera Survey observations for the UDG MATLAS-2019 in the NGC5846 group of galaxies. Using images in the $F606W$ and $F814W$ filters, we trace the GC population two magnitudes below the peak of the GC luminosity function. Employing Bayesian considerations, we find a total of 37$pm$5 GCs associated with the dwarf, which yields a large GC specific frequency of $S_N=84pm 12$. Due to the superior image quality of the HST, we are able to resolve the GCs and measure their sizes, which are consistent with the sizes of GCs from Local Group galaxies. Using the linear relation between the total mass of a galaxy and the total mass of GCs we derive a halo mass of $1.3pm0.2times10^{11}$ M$_odot$, corresponding to a mass-to-light ratio of over 1000. This suggests that either this UDG has an overly massive dark matter halo for its stellar mass, compared to other dwarfs -- though not as massive as the Milky Way -- or that the linear relation between the number of GCs and the dark matter halo mass breaks down for UDGs like MATLAS-2019. The high abundance of GCs, together with the small uncertainties, make MATLAS-2019 one of the most extreme UDGs, which likely sets an upper limit of the number of GCs for such objects.
We present FIRE/Gizmo hydrodynamic zoom-in simulations of isolated dark matter halos, two each at the mass of classical dwarf galaxies ($M_{rm vir} simeq 10^{10} M_{odot}$) and ultra-faint galaxies ($M_{rm vir} simeq 10^9 M_{odot}$), and with two feedback implementations. The resultant central galaxies lie on an extrapolated abundance matching relation from $M_{star} simeq 10^6$ to $10^4 M_{odot}$ without a break. Every host is filled with subhalos, many of which form stars. Our dwarfs with $M_{star} simeq 10^6 M_{odot}$ each have 1-2 well-resolved satellites with $M_{star} = 3-200 times 10^3 M_{odot}$. Even our isolated ultra-faint galaxies have star-forming subhalos. If this is representative, dwarf galaxies throughout the universe should commonly host tiny satellite galaxies of their own. We combine our results with the ELVIS simulations to show that targeting $sim 50~ rm kpc$ regions around nearby isolated dwarfs could increase the chances of discovering ultra-faint galaxies by $sim 35%$ compared to random halo pointings, and specifically identify the region around the Phoenix dwarf galaxy as a good potential target. The well-resolved ultra-faint galaxies in our simulations ($M_{star} simeq 3 - 30 times 10^3 M_{odot}$) form within $M_{rm peak} simeq 0.5 - 3 times 10^9 M_{odot}$ halos. Each has a uniformly ancient stellar population ($ > 10~ rm Gyr$) owing to reionization-related quenching. More massive systems, in contrast, all have late-time star formation. Our results suggest that $M_{rm halo} simeq 5 times 10^9 M_{odot}$ is a probable dividing line between halos hosting reionization fossils and those hosting dwarfs that can continue to form stars in isolation after reionization.
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{deg} 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.
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