Dwarf Satellite Galaxies Research Articles

The Mysterious Radcliffe Wave

The review is devoted to the Radcliffe Wave recently discovered by Alves et al. from the analysis of molecular clouds. These authors singled out a narrow chain of molecular clouds, elongated almost in one line, located at an inclination of about 30$^o$ to the galactic axis y. The Radcliffe Wave itself describes damped vertical oscillations of molecular clouds with a maximum oscillation amplitude of about 160 pc and a characteristic wavelength of about 2.5 kpc. To date, the presence of the Radcliffe Wave has been confirmed in the vertical distribution of a) interstellar dust, b) sources of maser radiation and radio stars, which are very young stars and protostars closely associated with molecular clouds, c) low-mass stars of the T Tau type, d) more massive OB stars and e) young open clusters of stars. The Radcliffe Wave is also traced in the vertical velocities of young stars. Most of the considered results of the analysis of the vertical velocities of various young stars show that the oscillations of the vertical positions and vertical velocities of stars in the Radcliffe Wave occur synchronously. The nature of the Radcliffe Wave is completely unclear. The majority of researchers associate its occurrence with the assumption of an external gravitational impact on the galactic disk of a striker such as a dwarf satellite galaxy of the Milky Way.

Classification of gamma-ray targets for velocity-dependent and subhalo-boosted dark-matter annihilation

Gamma-ray observations have long been used to constrain the properties of dark matter (DM), with a strong focus on weakly interacting massive particles annihilating through velocity-independent processes. However, in the absence of clear-cut observational evidence for the simplest candidates, the interest of the community in more complex DM scenarios involving a velocity-dependent cross-section has been growing steadily over the past few years. We present the first systematic study of velocity-dependent DM annihilation (in particular p-wave annihilation and Sommerfeld enhancement) in a variety of astrophysical objects, not only including the well-studied Milky Way dwarf satellite galaxies, but nearby dwarf irregular galaxies and local galaxy clusters as well. Particular attention is given to the interplay between velocity dependence and DM halo substructure. Uncertainties related to halo mass, phase-space and substructure modelling are also discussed in this velocity-dependent context. We show that, for s-wave annihilation, extremely large subhalo boost factors are to be expected, up to 1011 in clusters and up to 106–107 in dwarf galaxies where subhalos are usually assumed not to play an important role. Boost factors for p-wave annihilation are smaller but can still reach 103 in clusters. The angular extension of the DM signal is also significantly impacted, with e.g. the cluster typical emission radius increasing by a factor of order 10 in the s-wave case. We also compute the signal contrast of the objects in our sample with respect to annihilation happening in the Milky Way halo. Overall, we find that the hierarchy between the brightest considered targets depends on the specific details of the assumed particle-physics model.

The galaxy-wide stellar initial mass function in the presence of cluster-to-cluster IMF variations

We calculate the stellar integrated galactic initial mass function (IGIMF) in the presence of cluster-to-cluster variations of the IMF. Variations of the IMF for a population of coeval clusters that populate the initial cluster mass function (ICLMF) are taken into account in the form of Gaussian distribution functions of the IMF parameters. For the tapered power-law function used in this work, these are the slope at the high-mass end, Γ, the slope at the low-mass end, γ, and the characteristic mass Mch. The level of variations is modeled by varying the width of the Gaussian distributions. The reference values are the standard deviations of the parameters observed for the population of young clusters in the present-day Milky Way, which are σΓ = 0.6, σγ = 0.25, and σMch = 0.27 M⊙. We find that increasing the levels of dispersion for γ and Γ tends to moderately flatten the IGIMF at the low and high-mass end, respectively. The characteristic mass of the IGIMF is, however, strongly impacted by variations in Mch. Increasing the value of σMch shifts the peak of the IGIMF to lower masses, rendering the IGIMF more bottom heavy. This can provide a simple explanation for the bottom-heavy stellar mass function that is inferred for early-type galaxies since these are likely the result of a merger of disk galaxies where the physical conditions of the star-forming gas may vary significantly both in time and space in the merging system. The effect of IMF variations on the IGIMF is compared to the effects of other processes and sources of systematic variations such as those due to variations in the shape of ICLMF, the gas-phase metallicity, and the galactic star formation rate (SFR) which can potentially affect the maximum mass of stellar clusters in a galaxy and set the mean value of the characteristic mass in clusters. For the various dependencies we have explored, we found that the effect of IMF variations is a dominant factor that always affects the characteristic mass of the IGIMF. For the regimes at low metallicity where the IGIMF resembles a single power law, an increased level of IMF variations renders the IGIMF steeper and more bottom heavy, especially at low SFRs. On the other hand, variations in the IMF in the high mass regime can be easily dominated by variations in the slope of the ICLMF. We compare our results of the metallicity and SFR-dependent IGIMF to a sample of Milky Way ultra-faint dwarf (UFD) satellite galaxies that have available metallicity measurements. The present-day stellar mass function of these galaxies is a good analog to the IGIMF at the time their overall population of stars formed. We show that the slope of the stellar mass function of the UFD galaxies measured for stars in the mass range [0.4, 0.8] M⊙ can only be reproduced when IMF variations of the same order as those measured in the present-day Milky Way are included. Our results suggest that the inclusion of IMF variations in models of galaxy formation and evolution is of vital importance in order to improve our understanding of star formation and star formation feedback effects on galactic scales.

Forward-modelling the luminosity, distance, and size distributions of the Milky Way satellites

ABSTRACT We use GRUMPY, a simple regulator-type model for dwarf galaxy formation and evolution, to forward model the dwarf galaxy satellite population of the Milky Way (MW) using the Caterpillar zoom-in simulation suite. We show that luminosity and distance distributions of the model satellites are consistent with the distributions measured in the DES, PS1, and SDSS surveys, even without including a model for the orphan galaxies. We also show that our model for dwarf galaxy sizes can simultaneously reproduce the observed distribution of stellar half-mass radii, r1/2, of the MW satellites and the overall r1/2–M⋆ relation exhibited by observed dwarf galaxies. The model predicts that some of the observed faint stellar systems with r1/2 < 10 pc are ultra-faint dwarf galaxies. Scaling of the stellar mass M⋆ and peak halo mass Mpeak for the model satellites is not described by a power law, but has a clear flattening of M⋆–Mpeak scaling at $M_{\rm peak}\lt 10^8\, \, M_{\odot }$ imprinted by reionization. As a result, the fraction of low mass haloes ($M_{\rm peak}\lt 10^8 \, M_{\odot }$) hosting galaxies with MV < 0 is predicted to be 50 per cent at $M_{\rm peak}\sim 3.6 \times 10^7\, \, M_{\odot }$. We find that such high fraction at that halo mass helps to reproduce the number of dwarf galaxies discovered recently in the HSC-SSP survey. Using the model we forecast that there should be the total of $440^{+201}_{-147}$ (68 per cent confidence interval) MW satellites with MV < 0 and r1/2 > 10 pc within 300 kpc and make specific predictions for the HSC-SSP, DELVE-WIDE, and LSST surveys.

The Missing Satellite Problem outside of the Local Group. II. Statistical Properties of Satellites of Milky Way–like Galaxies

We present a new observation of satellite galaxies around seven Milky Way (MW)–like galaxies located outside of the Local Group (LG) using Subaru/Hyper Suprime-Cam imaging data to statistically address the missing satellite problem. We select satellite galaxy candidates using magnitude, surface brightness, Sérsic index, axial ratio, FWHM, and surface brightness fluctuation cuts, followed by visual screening of false positives such as optical ghosts of bright stars. We identify 51 secure dwarf satellite galaxies within the virial radius of nine host galaxies, two of which are drawn from the pilot observation presented in Paper I. We find that the average luminosity function of the satellite galaxies is consistent with that of the MW satellites, although the luminosity function of each host galaxy varies significantly. We observe an indication that more massive hosts tend to have a larger number of satellites. Physical properties of the satellites such as the size–luminosity relation are also consistent with the MW satellites. However, the spatial distribution is different; we find that the satellite galaxies outside of the LG show no sign of concentration or alignment, while that of the MW satellites is more concentrated around the host and exhibits a significant alignment. As we focus on relatively massive satellites with M V < −10, we do not expect that the observational incompleteness can be responsible here. This trend might represent a peculiarity of the MW satellites, and further work is needed to understand its origin.

H i properties of satellite galaxies around local volume hosts

ABSTRACT We present neutral atomic hydrogen (H i) observations using the Robert C. Byrd Green Bank Telescope along the lines of sight to 49 confirmed or possible dwarf satellite galaxies around eight Local Volume systems (M104, M51, NGC 1023, NGC 1156, NGC 2903, NGC 4258, NGC 4565, and NGC 4631). We detect the H i reservoirs of two candidates (dw0934+2204 and dw1238−1122) and find them to be background sources relative to their nearest foreground host systems. The remaining 47 satellite candidates are not detected in H i, and we place stringent 5σ upper limits on their H i mass. We note that some (15/47) of our non-detections stem from satellites being occluded by their putative host’s H i emission. In addition to these new observations, we compile literature estimates on the H i mass for an additional 17 satellites. We compare the H i properties of these satellites to those within the Local Group, finding broad agreement between them. Crucially, these observations probe a ‘transition’ region between −10 ≳ MV ≳ −14 where we see a mixture of gas-rich and gas-poor satellites. While there are many gas-poor satellites within this region, some are gas-rich and this suggests that the transition towards predominantly gas-rich satellites occurs at LV ∼ 107L⊙, in line with simulations. The observations presented here are a key step toward characterizing the properties of dwarf satellite galaxies around Local Volume systems and future wide-field radio surveys with higher angular resolution (e.g. WALLABY) will vastly improve upon the study of such systems.

The halo of M 105 and its group environment as traced by planetary nebula populations

Context. M 105 (NGC 3379) is an early-type galaxy in the nearby Leo I group, the closest galaxy group to contain all galaxy types and therefore an excellent environment to explore the low-mass end of intra-group light (IGL) assembly. Aims. We present a new and extended kinematic survey of planetary nebulae (PNe) in M 105 and the surrounding 30′×30′ in the Leo I group with the Planetary Nebula Spectrograph (PN.S) to investigate kinematically distinct populations of PNe in the halo and the surrounding IGL. Methods. We use PNe as kinematic tracers of the diffuse stellar light in the halo and IGL, and employ photo-kinematic Gaussian mixture models to (i) separate contributions from the companion galaxy NGC 3384, and (ii) associate PNe with structurally defined halo and IGL components around M 105. Results. We present a catalogue of 314 PNe in the surveyed area and firmly associate 93 of these with the companion galaxy NGC 3384 and 169 with M 105. The PNe in M 105 are further associated with its halo (138) and the surrounding exponential envelope (31). We also construct smooth velocity and velocity dispersion fields and calculate projected rotation, velocity dispersion, and λR profiles for the different components. PNe associated with the halo exhibit declining velocity dispersion and rotation profiles as a function of radius, while the velocity dispersion and rotation of the exponential envelope increase notably at large radii. The rotation axes of these different components are strongly misaligned. Conclusions. Based on the kinematic profiles, we identify three regimes with distinct kinematics that are also linked to distinct stellar population properties: (i) the rotating core at the centre of the galaxy (within 1Reff) formed in situ and is dominated by metal-rich ([M/H] ≈ 0) stars that also likely formed in situ, (ii) the halo from 1 to 7.5Reff consisting of a mixture of intermediate-metallicity and metal-rich stars ([M/H] &gt; −1), either formed in situ or was brought in via major mergers, and (iii) the exponential envelope reaching beyond our farthest data point at 16Reff, predominately composed of metal-poor ([M/H] &lt; −1) stars. The high velocity dispersion and moderate rotation of the latter are consistent with those measured for the dwarf satellite galaxies in the Leo I group, indicating that this exponential envelope traces the transition to the IGL.

The PAndAS View of the Andromeda Satellite System. III. Dwarf Galaxy Detection Limits

We determine the detection limits of the search for dwarf galaxies in the Pan-Andromeda Archaeological Survey (PAndAS) using the algorithm developed by the PAndAS team. The recovery fractions of artificial dwarf galaxies are, as expected, a strong function of physical size and luminosity and, to a lesser extent, distance. We show that these recovery fractions vary strongly with location in the surveyed area because of varying levels of contamination from both the Milky Way foreground stars and the stellar halo of Andromeda. We therefore provide recovery fractions that are a function of size, luminosity, and location within the survey on a scale of ∼1 × 1 deg2 (or ∼14 × 14 kpc2). Overall, the effective surface brightness for a 50% detection rate ranges between 28 and 30 mag arcsec−2. This is in line with expectations for a search that relies on photometric data that are as deep as the PAndAS survey. The derived detection limits are an essential ingredient on the path to constraining the global properties of Andromeda’s system of satellite dwarf galaxies and, more broadly, to providing constraints on dwarf galaxy formation and evolution in a cosmological context.

Quantum Tunneling of Fuzzy Dark Matter out of Satellite Galaxies

I show that the tidal gravitational potential of the Milky Way galaxy removes fuzzy dark matter from its satellite dwarf galaxies through quantum-mechanical tunneling. The existence of dark matter in satellites rules-out ultra-light axions as dark matter with a particle mass, m a < 2 × 10−21 eV. This limit exceeds the canonical mass range proposed as a solution to the small-scale challenges of the cold-dark-matter paradigm.

The Cen A galaxy group: Dynamical mass and missing baryons

The nearby elliptical galaxy Centaurus A (Cen A) is surrounded by a flattened system of dwarf satellite galaxies with coherent motions. Using a novel Bayesian approach, we measured the mean rotation velocity vrot and velocity dispersion σint of the satellite system. We found vrot/σint ≃ 0.7, indicating that the satellite system has non-negligible rotational support. Using Jeans’ equations, we measured a circular velocity of 258 km s−1 and a dynamical mass of 1.2 × 1013 M⊙ within 800 kpc. In a Λ cold dark matter cosmological context, we found that the Cen A group has a baryon fraction Mb/M200 ≃ 0.035 and is missing ∼77% of the cosmologically available baryons. Consequently, Cen A should have a hot intergalactic medium with a mass of ∼8 × 1011 M⊙, which is more than ∼20 times larger than current X-ray estimates. Intriguingly, the whole Cen A group lies on the baryonic Tully-Fisher relation defined by individual rotationally supported galaxies, as expected in Milgromian dynamics (MOND) with no need of missing baryons.

The escape of globular clusters from the satellite dwarf galaxies of the Milky Way

ABSTRACT Using numerical simulations, we have studied the escape of globular clusters (GCs) from the satellite dwarf spheroidal galaxies (dSphs) of the Milky Way (MW). We start by following the orbits of a large sample of GCs around dSphs in the presence of the MW potential field. We then obtain the fraction of GCs leaving their host dSphs within a Hubble time. We model dSphs by a Hernquist density profile with masses between $10^7$ and $7\times 10^9\, \mathrm{M}_{\odot }$. All dSphs lie on the Galactic disc plane, but they have different orbital eccentricities and apogalactic distances. We compute the escape fraction of GCs from 13 of the most massive dSphs of the MW, using their realistic orbits around the MW (as determined by Gaia). The escape fraction of GCs from 13 dSphs is in the range $12{{\ \rm per\ cent}}$ to $93{{\ \rm per\ cent}}$. The average escape time of GCs from these dSphs was less than 8 $\, \mathrm{Gyr}$, indicating that the escape process of GCs from dSphs was over. We then adopt a set of observationally constrained density profiles for specific case of the Fornax dSph. According to our results, the escape fraction of GCs shows a negative correlation with both the mass and the apogalactic distance of the dSphs, as well as a positive correlation with the orbital eccentricity of dSphs. In particular, we find that the escape fraction of GCs from the Fornax dSph is between $13{{\ \rm per\ cent}}$ and $38{{\ \rm per\ cent}}$. Finally, we observe that when GCs leave their host dSphs, their final orbit around the MW does not differ much from their host dSphs.

The effects of LMC-mass environments on their dwarf satellite galaxies in the FIRE simulations

ABSTRACTCharacterizing the predicted environments of dwarf galaxies like the Large Magellanic Cloud (LMC) is becoming increasingly important as next-generation surveys push sensitivity limits into this low-mass regime at cosmological distances. We study the environmental effects of LMC-mass haloes (M200m ∼ 1011 M⊙) on their populations of satellites (M⋆ ≥ 104 M⊙) using a suite of zoom-in simulations from the Feedback In Realistic Environments (FIRE) project. Our simulations predict significant hot coronas with T ∼ 105 K and Mgas ∼ 109.5 M⊙. We identify signatures of environmental quenching in dwarf satellite galaxies, particularly for satellites with intermediate mass (M⋆ = 106–107 M⊙). The gas content of such objects indicates ram pressure as the likely quenching mechanism, sometimes aided by star formation feedback. Satellites of LMC-mass hosts replicate the stellar mass dependence of the quiescent fraction found in satellites of Milky Way-mass hosts (i.e. that the quiescent fraction increases as stellar mass decreases). Satellites of LMC-mass hosts have a wider variety of quenching times when compared to the strongly bimodal distribution of quenching times of nearby centrals. Finally, we identify significant tidal stellar structures around four of our six LMC analogues, suggesting that stellar streams may be common. These tidal features originated from satellites on close orbits, extend to ∼80 kpc from the central galaxy, and contain ∼106–107 M⊙ of stars.

Dependence of stellar substructures in M31 type galaxy on satellite morphology in galaxy mergers

Stellar streams and shells are observed in halos of spiral galaxies. In this paper, we investigated the formation of these structures due to mergers between the host spiral galaxy and its dwarf satellite galaxies. We run the N-body simulations with two morphological models of a dwarf galaxy for different initial positions. One model is a spheroidal dwarf, dSph, and the other is a dwarf with a disk. We found that both models form stellar shells and streams and, in the case of the progenitor with a disk, streams are more prominent. After several pericentric passages, there is a possibility of formation of several streams. The remnant of the progenitor is more likely to disrupt later into the merger in the case of spiral progenitor than in the case of dSph.

Evolution of C iv Absorbers. II. Where Does C iv Live?

Abstract We use the observed cumulative statistics of C iv absorbers and dark matter halos to infer the distribution of C iv-absorbing gas relative to galaxies at redshifts 0 ≤ z ≤ 5. We compare the cosmic incidence dN/dX of C iv absorber populations and galaxy halos, finding that massive L ≥ L ⋆ halos alone cannot account for all the observed W r ≥ 0.05 Å absorbers. However, the dN/dX of lower-mass halos exceeds that of W r ≥ 0.05 Å absorbers. We also estimate the characteristic gas radius of absorbing structures required for the observed C iv dN/dX, assuming each absorber is associated with a single galaxy halo. The W r ≥ 0.3 Å and W r ≥ 0.6 Å C iv gas radii are ∼30%–70% (∼20%–40%) of the virial radius of L ⋆ (0.1L ⋆) galaxies, and the W r ≥ 0.05 Å gas radius is ∼100%–150% (∼60%–100%) of the virial radius of L ⋆ (0.1L ⋆) galaxies. For stronger absorbers, the gas radius relative to the virial radius rises across Cosmic Noon and falls afterwards, while for weaker absorbers, the relative gas radius declines across Cosmic Noon and then dramatically rises at z &lt; 1. A strong luminosity-dependence of the gas radius implies highly extended C iv envelopes around massive galaxies before Cosmic Noon, while a luminosity-independent gas radius implies highly extended envelopes around dwarf galaxies after Cosmic Noon. From available absorber-galaxy and C iv evolution data, we favor a scenario in which low-mass galaxies enrich the volume around massive galaxies at early epochs and propose that the outer halo gas (&gt;0.5 R v ) was produced primarily in ancient satellite dwarf galaxy outflows, while the inner halo gas (&lt;0.5 R v ) originated from the central galaxy and persists as recycled accreting gas.

The effect of dwarf galaxies on the tidal tails of globular clusters

ABSTRACT The tidal tails of globular clusters have been shown to be sensitive to the external tidal field. We investigate how Galactic globular clusters with observed tails are affected by satellite dwarf galaxies by simulating tails in galaxy models with and without dwarf galaxies. The simulations indicate that tidal tails can be subdivided into three categories based on how they are affected by dwarf galaxies: (1) dwarf galaxies perturb the progenitor cluster’s orbit (NGC 4590, Pal 1, Pal 5), (2) dwarf galaxies perturb the progenitor cluster’s orbit and individual tail stars (NGC 362, NGC 1851, NGC 4147, NGC 5466, NGC 7492, Pal 14, Pal 15), and (3) dwarf galaxies negligibly affect tidal tails (NGC 288, NGC 5139, NGC 5904, Eridanus). Perturbations to a cluster’s orbit occur when dwarf galaxies pass within its orbit, altering the size and shape of the orbital and tail path. Direct interactions between one or more dwarf galaxies and tail stars lead to kinks and spurs, however we find that features are more difficult to observe in projection. We further find that the tails of Pal 5 are shorter in the galaxy model with dwarf galaxies as it is closer to apocentre, which results in the tails being compressed. Additional simulations reveal that differences between tidal tails in the two galaxy models are primarily due to the Large Magellanic Cloud. Understanding how dwarf galaxies affect tidal tails allows for tails to be used to map the distribution of matter in dwarf galaxies and the Milky Way.

Orbits of 47 dwarf satellite galaxies of the MilkyWay in three models of the gravitational potential with different masses

Orbits of 47 dwarf satellite galaxies of the MilkyWay in three models of the gravitational potential with different masses

Probing PeV scale SUSY breaking with satellite galaxies and primordial gravitational waves

We study an inevitable cosmological consequence in PeV scale SUSY-breaking scenarios. We focus on the SUSY-breaking scale corresponding to the gravitino mass $m_{3/2}=100{\rm eV}-1{\rm keV}$. We argue that the presence of an early matter-dominated era and the resulting entropy production are requisite for the Universe with this gravitino mass. We infer the model-independent minimum amount of the entropy production $\Delta$ by requiring that the number of dwarf satellite galaxies $N_{\rm sat}$ in the Milky Way exceed the currently observed value, i.e. $N_{\rm sat}\gtrsim63$. This entropy production is inevitably imprinted on the primordial gravitational waves (pGWs) produced during the inflationary era. We study how the information on the value of $\Delta$ and the time of entropy production are encoded in the pGW spectrum $\Omega_{\rm GW}$. If the future GW surveys observe a suppression feature in the pGW spectrum for the frequency range $\mathcal{O}(10^{-10}){\rm Hz}\lesssim f_{\rm GW}\lesssim\mathcal{O}(10^{-5}){\rm Hz}$, it works as a smoking gun for PeV SUSY-breaking scenarios. Even if they do not, our study can be used to rule out all such scenarios.

Gravitational Lensing by a Massive Object in a Dark Matter Halo. I. Critical Curves and Caustics

Abstract We study the gravitational lensing properties of a massive object in a dark matter halo, concentrating on the critical curves and caustics of the combined lens. We model the system in the simplest approximation by a point mass embedded in a spherical Navarro–Frenk–White density profile. The low number of parameters of such a model permits a systematic exploration of its parameter space. We present galleries of critical curves and caustics for different masses and positions of the point in the halo. We demonstrate the existence of a critical mass, above which the gravitational influence of the centrally positioned point is strong enough to eliminate the radial critical curve and caustic of the halo. In the point-mass parameter space we identify the boundaries at which critical-curve transitions and corresponding caustic metamorphoses occur. The number of transitions as a function of the position of the point is surprisingly high, ranging from three for higher masses to as many as eight for lower masses. On the caustics we identify the occurrence of six different types of caustic metamorphoses. We illustrate the peculiar properties of the single radial critical curve and caustic appearing in an additional unusual nonlocal metamorphosis for a critical mass positioned at the halo center. Although we construct the model primarily to study the lensing influence of individual galaxies in a galaxy cluster, it can also be used to study the lensing by dwarf satellite galaxies in the halo of a host galaxy, as well as (super)massive black holes at a general position in a galactic halo.

NGC 147 Corroborates the Break in the Stellar Mass–Stellar Metallicity Relation for Galaxies

Abstract The stellar mass–stellar metallicity relation (MZR) is an essential approach to probing the chemical evolution of galaxies. It reflects the balance between galactic feedback and gravitational potential as a function of stellar mass. However, the current MZR of local dwarf satellite galaxies (M * ≲ 108 M ⊙; measured from resolved stellar spectroscopy) may not be reconcilable with that of more massive galaxies (M * ≳ 109.5 M ⊙; measured from integrated-light spectroscopy). Such a discrepancy may result from a systematic difference between the two methods, or it may indicate a break in the MZR around 109 M ⊙. To address this question, we measured the stellar metallicity of NGC 147 from integrated light using the Palomar Cosmic Web Imager. We compared the stellar metallicity estimates from integrated light with measurements from resolved stellar spectroscopy and found them to be consistent within 0.1 dex. On the other hand, the high-mass MZR overpredicts the metallicity by 0.6 dex at the mass of NGC 147. Therefore, our results tentatively suggest that the discrepancy between the low-mass MZR and high-mass MZR should not be attributed to a systematic difference in techniques. Instead, real physical processes cause the transition in the MZR. In addition, we discovered a positive age gradient in the innermost region and a negative metallicity gradient from the resolved stars at larger radii, suggesting a possible outside-in formation of NGC 147.

A search for satellite galaxies of nearby star-forming galaxies with resolved stars in LBT-SONG

ABSTRACT We present results from a resolved stellar population search for dwarf satellite galaxies of six nearby (D &amp;lt; 5 Mpc), sub-Milky Way mass hosts using deep (m ∼ 27 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 catalogue-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 MV &amp;lt; −12 that lie in our survey volume. We preview a new theoretical framework to predict satellite luminosity functions using analytical probability distribution functions and apply it to our sample, finding that we predict one fewer classical dwarf and one more faint dwarf (MV ∼ −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.