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1. New dwarf galaxy candidates in the sphere of influence of the Sombrero galaxy

   https://doi.org/10.1093/mnras/stad3741  

   Crosby, Ethan; Jerjen, Helmut; Müller, Oliver; Pawlowski, Marcel S; Mateo, Mario; Lelli, Federico (November 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We report the discovery of 40 new satellite dwarf galaxy candidates in the sphere of influence of the Sombrero Galaxy (M104), the most luminous galaxy in the Local Volume. Using the Subaru Hyper Suprime-Cam, we surveyed 14.4 deg2 of its surroundings, extending to the virial radius. Visual inspection of the deep images and galfit modelling yielded a galaxy sample highly complete down to Mg ∼ −9 ($$L_{g}\sim 3\times 10^{5}\ \mathrm{ L}_\odot$$) and spanning magnitudes −16.4 < Mg < −8 and half-light radii 50 pc < re < 1600 pc assuming the distance of M104. These 40 new candidates, out of which 27 are group members with high confidence, double the number of potential satellites of M104 within the virial radius, placing it among the richest hosts in the Local Volume. Using a principal component analysis, we find that the entire sample of candidates is consistent with an almost circular on-sky distribution, more circular than any comparable environment found in the Illustris TNG100-1 (The Next Generation) simulation. However, the distribution of the high-probability sample is more oblate and consistent with the simulation. The cumulative satellite luminosity function is broadly consistent with analogues from the simulation, albeit it contains no bright satellite with Mg < −16.4 ($$L_{g}\sim 3 \times 10^{8}\ \mathrm{ L}_\odot$$), a $$2.3\, \sigma$$ occurrence. Follow-up spectroscopy to confirm group membership will begin to demonstrate how these systems can act as probes of the structure and formation history of the halo of M104. 

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2. A Census of Dwarf Galaxy Satellites around LMC-mass Galaxy NGC 2403*

   https://doi.org/10.3847/1538-4357/ad8dcd  

   Carlin, Jeffrey_L; Sand, David_J; Mutlu-Pakdil, Burçin; Crnojević, Denija; Doliva-Dolinsky, Amandine; Garling, Christopher_T; Peter, Annika_H_G; Brodie, Jean_P; Forbes, Duncan_A; Hargis, Jonathan_R; et al (December 2024, The Astrophysical Journal)

   Abstract We present the first comprehensive census of the satellite population around a Large Magellanic Cloud stellar-mass galaxy, as part of the Magellanic Analog Dwarf Companions and Stellar Halos (MADCASH) survey. We have surveyed NGC 2403 (D= 3.0 Mpc) with the Subaru/Hyper Suprime-Cam imager out to a projected radius of 90 kpc (with partial coverage extending out to ∼110 kpc, or ∼80% of the virial radius of NGC 2403), resolving stars in the uppermost ∼2.5 mag of its red giant branch. By looking for stellar overdensities in the red giant branch spatial density map, we identify 149 satellite candidates, of which only the previously discovered MADCASH J074238+65201-dw is a bona fide dwarf, together with the more massive and disrupting satellite DDO 44. We carefully assess the completeness of our search via injection of artificial dwarf galaxies into the images, finding that we are reliably sensitive to candidates down toM_V∼ −7.5 mag (and somewhat sensitive to even fainter satellites). A comparison of the satellite luminosity function of NGC 2403 down to this magnitude limit to theoretical expectations shows overall good agreement. This is the first of a full sample of 11 Magellanic Cloud–mass host galaxies we will analyze, creating a statistical sample that will provide the first quantitative constraints on hierarchical models of galaxy formation around low-mass hosts. 

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3. Accretion of galaxy groups into galaxy clusters

   https://doi.org/10.1093/mnras/staa2636  

   Benavides, José A; Sales, Laura V; Abadi, Mario G (September 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We study the role of group infall in the assembly and dynamics of galaxy clusters in ΛCDM. We select 10 clusters with virial mass M200 ∼ 1014 $$\rm M_\odot$$ from the cosmological hydrodynamical simulation Illustris and follow their galaxies with stellar mass M⋆ ≥ 1.5 × 108 $$\rm M_\odot$$. A median of $${\sim}38{{\ \rm per\ cent}}$$ of surviving galaxies at z = 0 is accreted as part of groups and did not infall directly from the field, albeit with significant cluster-to-cluster scatter. The evolution of these galaxy associations is quick, with observational signatures of their common origin eroding rapidly in 1–3 Gyr after infall. Substructure plays a dominant role in fostering the conditions for galaxy mergers to happen, even within the cluster environment. Integrated over time, we identify (per cluster) an average of 17 ± 9 mergers that occur in infalling galaxy associations, of which 7 ± 3 occur well within the virial radius of their cluster hosts. The number of mergers shows large dispersion from cluster to cluster, with our most massive system having 42 mergers above our mass cut-off. These mergers, which are typically gas rich for dwarfs and a combination of gas rich and gas poor for M⋆ ∼ 1011 $$\rm M_\odot$$, may contribute significantly within ΛCDM to the formation of specific morphologies, such as lenticulars (S0) and blue compact dwarfs in groups and clusters. 

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4. The hestia project: simulations of the Local Group

   https://doi.org/10.1093/mnras/staa2541  

   Libeskind, Noam I; Carlesi, Edoardo; Grand, Robert J; Khalatyan, Arman; Knebe, Alexander; Pakmor, Ruediger; Pilipenko, Sergey; Pawlowski, Marcel S; Sparre, Martin; Tempel, Elmo; et al (September 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present the hestia simulation suite: High-resolutions Environmental Simulations of The Immediate Area, a set of cosmological simulations of the Local Group. Initial conditions constrained by the observed peculiar velocity of nearby galaxies are employed to accurately simulate the local cosmography. Halo pairs that resemble the Local Group are found in low resolutions constrained, dark matter only simulations, and selected for higher resolution magneto hydrodynamic simulation using the arepo code. Baryonic physics follows the auriga model of galaxy formation. The simulations contain a high-resolution region of 3–5 Mpc in radius from the Local Group mid-point embedded in the correct cosmographic landscape. Within this region, a simulated Local Group consisting of a Milky Way and Andromeda like galaxy forms, whose description is in excellent agreement with observations. The simulated Local Group galaxies resemble the Milky Way and Andromeda in terms of their halo mass, mass ratio, stellar disc mass, morphology separation, relative velocity, rotation curves, bulge-disc morphology, satellite galaxy stellar mass function, satellite radial distribution, and in some cases, the presence of a Magellanic cloud like object. Because these simulations properly model the Local Group in their cosmographic context, they provide a testing ground for questions where environment is thought to play an important role. 

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5. Discovery of a red backsplash galaxy candidate near M81

   https://doi.org/10.1093/mnras/stad352  

   Casey, Kirsten J.; Greco, Johnny P.; Peter, Annika H. G.; Davis, A. Bianca (February 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Understanding quenching mechanisms in low-mass galaxies is essential for understanding galaxy evolution overall. In particular, isolated galaxies are important tools to help disentangle the complex internal and external processes that impact star formation. Comparisons between quenched field and satellite galaxies in the low-mass regime offer a substantial opportunity for discovery, although very few quenched galaxies with masses below $$M_{\star }\, \sim \, 10^{9} {\rm M}_{\odot }$$ are known outside the virial radius, Rvir, of any host halo. Importantly, simulations and observations suggest that an in-between population of backsplash galaxies also exists that may complement interpretations of environmental quenching. Backsplash galaxies – like field galaxies – reside outside the virial radius of a host halo, but their star formation can be deeply impacted by previous interactions with more massive systems. In this paper, we report the concurrent discovery of a low-mass ($$M_{\star }\, \sim \, 10^{7} {\rm M}_{\odot }$$) quenched galaxy approximately 1Rvir in projection from the M81 group. We use surface brightness fluctuations (SBF) to investigate the possibility that the new galaxy, dw0910+7326 (nicknamed Blobby), is a backsplash galaxy or a more distant field galaxy. The measured SBF distance of $$3.21\substack{+0.15 +0.41 \\-0.15 -0.36}$$ Mpc indicates that Blobby likely lies in the range 1.0 < R/Rvir < 2.7 outside the combined M81–M82 system. Given its distance and quiescence, Blobby is a good candidate for a backsplash galaxy and could provide hints about the formation and evolution of these interesting objects. 

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