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Quantifying the connection between galaxies and their host dark matter halos has been key for testing cosmological models on various scales. BelowM_⋆∼ 10⁹M_⊙, such studies have primarily relied on the satellite galaxy population orbiting the Milky Way (MW). Here we present new constraints on the connection between satellite galaxies and their host dark matter subhalos using the largest sample of satellite galaxies in the Local Volume (D≲ 12 Mpc) to date. We use 250 confirmed and 71 candidate dwarf satellites around 27 MW-like hosts from the Exploration of Local VolumE Satellites (ELVES) Survey and use the semianalyticalSatGenmodel for predicting the population of dark matter subhalos expected in the same volume. Through a Bayesian model comparison of the observed and the forward-modeled satellite stellar mass functions (SSMFs), we infer the satellite stellar-to-halo mass relation. We find that the observed SSMF is best reproduced when subhalos at the low-mass end are populated by a relation of the form$M_{\star }\propto M_{\mathrm{peak}}^{\alpha }$, with a moderate slope of${\alpha }_{\mathrm{const}}=2.10\pm 0.01$and a low scatter, constant as a function of the peak halo mass, of${\sigma }_{\mathrm{const}}={0.06}_{-0.05}^{+0.07}$. A model with a steeper slope (α_grow= 2.39 ± 0.06) and a scatter that grows with decreasingM_peakis also consistent with the observed SSMF but is not required. Our new model for the satellite–subhalo connection, based on hundreds of Local Volume satellite galaxies, is in line with what was previously derived using only MW satellites.

 

Globular clusters (GCs) provide valuable insight into the properties of their host galaxies’ dark matter halos. UsingN-body simulations incorporating semianalytic dynamical friction and GC−GC merger prescriptions, we study the evolution of GC radial distributions and mass functions in cuspy and cored dark matter halos. Modeling the dynamics of the GC-rich system in the dwarf galaxy UGC 7369, we find that friction-induced inspiral and subsequent mergers of massive GCs can naturally and robustly explain the mass segregation of the GCs and the existence of a nuclear star cluster (NSC). However, the multiple mergers required to form the NSC only take place when the dark matter halo is cuspy. In a cored halo, stalling of the dynamical friction within the core halts the inspiral of the GCs, and so the GC merger rate falls significantly, precluding the formation of an NSC. We therefore argue that the presence of an NSC requires a cusp in UGC 7369. More generally, we propose that the presence of an NSC and the corresponding alteration of the GC mass function due to mergers may be used as an indicator of a cuspy halo for galaxies in which we expect NSC formation to be merger dominated. These observables represent a simple, powerful complement to other inner halo density profile constraint techniques and should allow for straightforward extension to larger samples.

 

Recent observations have reignited interest in a population of dwarf galaxies that are large and diffuse for their mass, often called ultra-diffuse galaxies (UDGs). However, the origin and evolution of these mass–size outliers and the role of the environment are still unclear. Using the exquisitely deep and wide Hyper Suprime-Cam Strategic Survey images, we search for ultra-puffy galaxies (UPGs), defined as being 1.5σlarger than the average size for their mass, around Milky Way–like galaxies. We present the sizes and radial distributions of mass–size outliers and derive their quenched fraction to explore the impact of the environment. Surprisingly, despite being outliers in size, the UPGs have a similar quenched fraction as normal-sized satellites of Milky Way analogs in both observations and simulations, suggesting that quenching is not tied to being a mass–size outlier. The quenched fraction is higher for the UPGs associated with redder hosts, as well as those that are closer to the host in projection. In contrast, the UDGs are overall redder and more quiescent compared with normal satellites. We show that the classic definition of UDGs is heavily weighted toward quenched galaxies and thus cannot be used for a study of quenching of mass–size outliers.

 

Isolated dwarf galaxies usually exhibit robust star formation but satellite dwarf galaxies are often devoid of young stars, even in Milky Way–mass groups. Dwarf galaxies thus offer an important laboratory of the environmental processes that cease star formation. We explore the balance of quiescent and star-forming galaxies (quenched fractions) for a sample of ∼400 satellite galaxies around 30 Local Volume hosts from the Exploration of Local VolumE Satellites (ELVES) Survey. We present quenched fractions as a function of satellite stellar mass, projected radius, and host halo mass, to conclude that overall, the quenched fractions are similar to the Milky Way, dropping below 50% at satelliteM_*≈ 10⁸M_⊙. We may see hints that quenching is less efficient at larger radii. Through comparison with the semianalytic modeling codeSatGen, we are also able to infer average quenching times as a function of satellite mass in host halo-mass bins. There is a gradual increase in quenching time with satellite stellar mass rather than the abrupt change from rapid to slow quenching that has been inferred for the Milky Way. We also generally infer longer average quenching times than recent hydrodynamical simulations. Our results are consistent with models that suggest a wide range of quenching times are possible via ram pressure stripping, depending on the clumpiness of the circumgalactic medium, the orbits of the satellites, and the degree of earlier preprocessing.

 

Large diffuse galaxies are hard to find, but understanding the environments where they live, their numbers, and ultimately their origins, is of intense interest and importance for galaxy formation and evolution. Using Subaru’s Hyper Suprime-Cam Strategic Survey Program, we perform a systematic search for low surface brightness galaxies and present novel and effective methods for detecting and modeling them. As a case study, we surveyed 922 Milky Way analogs in the nearby Universe (0.01 <z< 0.04) and built a large sample of satellite galaxies that are outliers in the mass–size relation. These “ultra-puffy” galaxies (UPGs), defined to be 1.5σabove the average mass–size relation, represent the tail of the satellite size distribution. We find that each MW analog hostsN_UPG= 0.31 ± 0.05 UPGs on average, which is consistent with but slightly lower than the observed abundance at this halo mass in the Local Volume. We also construct a sample of ultra-diffuse galaxies (UDGs) in MW analogs and find an abundance ofN_UDG= 0.44 ± 0.05 per host. With literature results, we confirm that the UDG abundance scales with the host halo mass following a sublinear power law. We argue that our definition of UPGs, which is based on the mass–size relation, is more physically motivated than the common definition of UDGs, which depends on the surface brightness and size cuts and thus yields different surface mass density cuts for quenched and star-forming galaxies.

 

Abstract We present the discovery of a giant cloud of ionized gas in the field of the starbursting galaxy M82. Emission from the cloud is seen in H α and [N ii ] λ 6583 in data obtained though a small pathfinder instrument used to test the key ideas that will be implemented in the Dragonfly Spectral Line Mapper, an upcoming ultranarrow-bandpass imaging version of the Dragonfly Telephoto Array. The discovered cloud has a shell-like morphology with a linear extent of 0.°8 and is positioned 0.°6 northwest of M82. At the heliocentric distance of the M81 group, the cloud’s longest angular extent corresponds to 55 kpc and its projected distance from the nucleus of M82 is 40 kpc. The cloud has an average H α surface brightness of 2 × 10 −18 erg cm − 2 s − 1 arcsec − 2 . The [N ii ] λ 6583/H α line ratio varies from [N ii ]/H α ∼ 0.2 to [N ii ]/H α ∼ 1.0 across the cloud, with higher values found in its eastern end. Follow-up spectra obtained with Keck LRIS confirm the existence of the cloud and yield line ratios of [N ii ] λ 6583/H α = 0.340 ± 0.003 and [S ii ] λλ 6716, 6731/H α = 0.64 ± 0.03 in the cloud. This giant cloud of material could be lifted from M82 by tidal interactions or by its powerful starburst. Alternatively, it may be gas infalling from the cosmic web, potentially precipitated by the superwinds of M82. Deeper data are needed to test these ideas further. The upcoming Dragonfly Spectral Line Mapper will have 120 lenses, 40× more than in the pathfinder instrument used to obtain the data presented here. 

We present the primary results from the Dragonfly Edge-on Galaxies Survey, an exploration of the stellar halos of twelve nearby (d< 25 Mpc) edge-on disk galaxies with the Dragonfly Telephoto Array. The edge-on orientation of these galaxies allows their stellar halos to be explored with minimal obscuration by or confusion with the much brighter disk light. Galaxies in the sample span a range of stellar masses from 10^9.68to 10^10.88M_⊙. We confirm that the wide range of stellar halo mass fractions previously seen for Milky Way–mass galaxies is also found among less massive spiral galaxies. The scatter in stellar halo mass fraction is large, but we do find a significant positive correlation between stellar halo mass fraction and total stellar mass when the former is measured beyond five half-mass radii. Reasonably good agreement is found with predictions from cosmological hydrodynamical simulations, although observed stellar halo fractions appear to be somewhat lower than expected from these simulations.

 

We present the statistical redshift distribution of a large sample of low-surface-brightness (LSB) galaxies identified in the first 200 deg²of the Hyper Suprime-Cam Strategic Survey Program. Through cross-correlation with the NASA–SDSS Atlas, we find that the majority of objects lie withinz< 0.15 or ∼500 Mpc, yielding a mass range ofM_*≈ 10⁷−10⁹M_⊙and a size range ofr_eff,g≈ 1−8 kpc. We find a peak in the distance distribution within 100 Mpc, corresponding mostly to ∼10⁷M_⊙galaxies that fall on the known mass–size relation. There is also a tail in the redshift distribution out toz≈ 0.15, comprising more massive (M_*= 10⁸− 10⁹M_⊙) galaxies at the larger end of our size range. We see tentative evidence that at the higher-mass end (M_*> 10⁸M_⊙), the LSB galaxies do not form a smooth extension of the mass–size relation of higher-surface-brightness galaxies, perhaps suggesting that the LSB galaxy population is distinct in its formation path.

 

Two ultra-diffuse galaxies in the same group, NGC1052-DF2 and NGC1052-DF4, have been found to have little or no dark matter and to host unusually luminous globular cluster populations. Such low-mass diffuse objects in a group environment are easily disrupted and are expected to show evidence of tidal distortions. In this work, we present deep new imaging of the NGC1052 group, obtained with the Dragonfly Telephoto Array, to test this hypothesis. We find that both galaxies show strong position-angle twists and are significantly more elongated at their outskirts than in their interiors. The group’s central massive elliptical NGC1052 is the most likely source of these tidal disturbances. The observed distortions imply that the galaxies have a low total mass or are very close to NGC1052. Considering constraints on the galaxies’ relative distances, we infer that the dark matter halo masses of these galaxies cannot be much greater than their stellar masses. Calculating pericenters from the distortions, we find that the galaxies are on highly elliptical orbits, with a ratio of pericenter to present-day radiusR_peri/R₀∼ 0.1 if the galaxies are dark matter–free andR_peri/R₀∼ 0.01 if they have a normal dark halo. Our findings provide strong evidence, independent of kinematic constraints, that both galaxies are dark matter–deficient. Furthermore, the similarity of the tidal features in NGC1052-DF2 and NGC1052-DF4 strongly suggests that they arose at comparable distances from NGC1052. In Appendix A, we describesbcontrast, a robust method for determining the surface brightness limits of images.