We present high-resolution rotation curves and mass models of 26 dwarf galaxies from "Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey" (LITTLE THINGS). LITTLE THINGS is a high-resolution (∼6″ angular; <2.6 km s −1 velocity resolution) Very Large Array H I survey for nearby dwarf galaxies in the local volume within 11 Mpc. The high-resolution H I observations enable us to derive reliable rotation curves of the sample galaxies in a homogeneous and consistent manner. The rotation curves are then combined with Spitzer archival 3.6 μm and ancillary optical U, B, and V images to construct mass models of the galaxies. This high quality multi-wavelength data set significantly reduces observational uncertainties and thus allows us to examine the mass distribution in the galaxies in detail. We decompose the rotation curves in terms of the dynamical contributions by baryons and dark matter (DM) halos, and compare the latter with those of dwarf galaxies from THINGS as well as ΛCDM Smoothed Particle Hydrodynamic (SPH) simulations in which the effect of baryonic feedback processes is included. Being generally consistent with THINGS and simulated dwarf galaxies, most of the LITTLE THINGS sample galaxies show a linear increase of the rotation curve in their inner regions, which gives shallower logarithmic inner slopes α of their DM density profiles. The mean value of the slopes of the 26 LITTLE THINGS dwarf galaxies is α = − ± 0.32 0.24 which is in accordance with the previous results found for low surface brightness galaxies (α = − ± 0.2 0.2) as well as the seven THINGS dwarf galaxies (α = − ± 0.29 0.07). However, this significantly deviates from the cusp-like DM distribution predicted by DM-only ΛCDM simulations. Instead our results are more in line with the shallower slopes found in the ΛCDM SPH simulations of dwarf galaxies in which the effect of baryonic feedback processes is included. In addition, we discuss the central DM distribution of DDO 210 whose stellar mass is relatively low in our sample to examine the scenario of inefficient supernova feedback in low mass dwarf galaxies predicted from recent ΛCDM SPH simulations of dwarf galaxies where central cusps still remain.

We present a photometric study of the dwarf galaxy population in the core region (≲ r vir 4) of the Fornax galaxy cluster based on deep u ′ g ′ i ′ photometry from the Next Generation Fornax Cluster Survey. All imaging data were obtained with the Dark Energy Camera mounted on the 4-meter Blanco telescope at the Cerro-Tololo Interamerican Observatory. We identify 258 dwarf galaxy candidates with luminosities −17 ≲ M g ′ ≲ −8 mag, corresponding to typical stellar masses of 9.5 ≳ log M ⋆ M ⊙ ≳ 5.5, reaching ∼ 3 mag deeper in point-source luminosity and ∼4 mag deeper in surface-brightness sensitivity compared to the classic Fornax Cluster Catalog. Morphological analysis shows that the dwarf galaxy surface-brightness profiles are well represented by singlecomponent Sérsic models with average Sérsic indices of ⟨n⟩ u ′ ,g ′ ,i ′ = (0.78 − 0.83) ± 0.02, and average effective radii of ⟨r e ⟩ u ′ ,g ′ ,i ′ = (0.67 − 0.70) ± 0.02 kpc. Color-magnitude relations indicate a flattening of the galaxy red sequence at faint galaxy luminosities, similar to the one recently discovered in the Virgo cluster. A comparison with population synthesis models and the galaxy mass-metallicity relation reveals that the average faint dwarf galaxy is likely older than ∼5 Gyr. We study galaxy scaling relations between stellar mass, effective radius, and stellar mass surface density over a stellar mass range covering six orders of magnitude. We find that over the sampled stellar mass range several distinct mechanisms of galaxy mass assembly can be identified: i) dwarf galaxies assemble mass inside the half-mass radius up to log M ⋆ ≈ 8.0, ii) isometric mass assembly in the range 8.0 ≲ log M ⋆ M ⊙ ≲ 10.5, and iii) massive galaxies assemble stellar mass predominantly in their halos at log M ⋆ ≈10.5 and above.

Local Group (LG) galaxies have relatively accurate star formation histories (SFHs) and metallicity evolution derived from resolved color-magnitude diagram (CMD) modeling, and thus offer a unique opportunity to explore the efficacy of estimating stellar mass M of real galaxies based on the integrated stellar luminosities. Building on the SFHs and metallicity evolution of 40 LG dwarf galaxies, we carried out a comprehensive study of the influence of SFHs, metallicity evolution, and dust extinction on the UV-to-NIR color-mass-to-light-ratio (color-log Υ (λ)) distributions and M estimation of local universe galaxies. We find that: 1) The LG galaxies follow color-log Υ (λ) relations that fall in between the ones calibrated by previous studies; 2) Optical color-log Υ (λ) relations at higher [M/H] are generally broader and steeper; 3) The SFH shape parameter "concentration" does not significantly affect the color-log Υ (λ) relations; 4) Light-weighted ages age λ and metallicities [M/H] λ of galaxies are the closest analogs to ages and metallicities of single stellar populations, and the two together constrain log Υ (λ) with uncertainties ranging from 0.1 dex for the NIR up to 0.2 dex for the optical passbands; 5) Metallicity evolution induces significant uncertainties to the optical but not NIR Υ (λ) at given age λ and [M/H] λ ; 6) The V band is the ideal luminance passband for estimating Υ (λ) from single colors, because the combinations of Υ (V ) and optical colors such as B−V and g−r exhibit the weakest systematic dependences on SFHs, metallicities and dust extinction; 7) Without any prior assumption on SFHs, M is constrained with biases 0.3 dex by the UV-or optical-to-NIR SED fitting. Optical passbands alone constrain M with biases 0.4 dex (or 0.6 dex) when dust extinction is fixed (or variable) in SED fitting. SED fitting with monometallic SFH models tends to underestimate M of real galaxies. M tends to be overestimated (or underestimated) at the youngest (or oldest) age mass .

We present the analysis of 61 nucleated dwarf galaxies in the central regions ( R vir /4) of the Fornax galaxy cluster. The galaxies and their nuclei are studied as part of the Next Generation Fornax Survey (NGFS) using optical imaging obtained with the Dark Energy Camera (DECam) mounted at Blanco/CTIO and near-infrared data obtained with VIRCam at VISTA/ESO. We decompose the nucleated dwarfs in nucleus and spheroid, after subtracting the surface brightness profile of the spheroid component and studying the nucleus using PSF photometry. In general, nuclei are consistent with colors of confirmed metal-poor globular clusters, but with significantly smaller dispersion than other confirmed compact stellar systems in Fornax. We find a bimodal nucleus mass distribution with peaks located at log(M * /M ) 5.4 and ∼ 6.3. These two nucleus sub-populations have different stellar population properties, the more massive nuclei are older than ∼ 2 Gyr and have metal-poor stellar populations (Z ≤ 0.02 Z ), while the less massive nuclei are younger than ∼ 2 Gyr with metallicities in the range 0.02 < Z/Z ≤ 1. We find that the nucleus mass (M nuc ) vs. galaxy mass (M gal ) relation becomes shallower for less massive galaxies starting around 10 8 M and the mass ratio η n = M nuc /M gal shows a clear anti-correlation with M gal for the lowest masses, reaching 10%. We test current theoretical models of nuclear cluster formation and find that they cannot fully reproduce the observed trends. A likely mixture of in-situ star formation and star-cluster mergers seem to be acting during nucleus growth over cosmic time.

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To get a high-precision optical surface, the deconvolved process of dwell time was transferred to a matrix equation in which the damped factor and the extra removal amount were introduced to expand the freedom of solution. A path weight factor and a surface error weight factor were used to take the scanning path and the initial surface error into account. Combined with the Gerchberg bandlimited extrapolation algorithm for initial surface error map extension, a high-precision final surface could be obtained within a factual aperture. Two surface error maps were calculated to rms = 0.1 nm from rms = 130.23 nm and to rms = 0.08 nm from rms = 82.74 nm. The simulations show that a perfect dwell time solution could be obtained by the revised matrix equation and initial surface error map extension with the help of the least squares QR (LSQR) algorithm.

Intra-cluster (IC) populations are expected to be a natural result of the hierarchical assembly of clusters, yet their low space densities make them difficult to detect and study. We present the first definitive kinematic detection of an IC population of globular clusters (GCs) in the Virgo cluster, around the central galaxy, M87. This study focuses on the Virgo core for which the combination of NGVS photometry and follow-up spectroscopy allows us to reject foreground star contamination and explore GC kinematics over the full Virgo dynamical range. The GC kinematics changes gradually with galactocentric distance, decreasing in mean velocity and increasing in velocity dispersion, eventually becoming indistinguishable from the kinematics of Virgo dwarf galaxies at R > 320 kpc. By kinematically tagging M87 halo and intra-cluster GCs we find that 1) the M87 halo has a smaller fraction (52 ± 3%) of blue clusters with respect to the IC counterpart (77 ± 10%), 2) the (g − r ) 0 vs (i − z ) 0 color-color diagrams reveal a galaxy population that

We derive stellar population parameters for a representative sample of ultracompact dwarfs (UCDs) and a large sample of massive globular clusters (GCs) with stellar masses 10 6 M ⊙ in the central galaxy M87 of the Virgo galaxy cluster, based on model fitting to the Lick-index measurements from both the literature and new observations. After necessary spectral stacking of the relatively faint objects in our initial sample of 40 UCDs and 118 GCs, we obtain 30 sets of Lick-index measurements for UCDs and 80 for GCs. The M87 UCDs have ages 8 Gyr and [α/Fe] ≃ 0.4 dex, in agreement with previous studies based on smaller samples. The literature UCDs, located in lower-density environments than M87, extend to younger ages and smaller [α/Fe] (at given metallicities) than M87 UCDs, resembling the environmental dependence of the Virgo dE nuclei. The UCDs exhibit a positive mass-metallicity relation (MZR), which flattens and connects compact ellipticals at stellar masses 10 8 M ⊙ . The Virgo dE nuclei largely follow the average MZR of UCDs, whereas most of the M87 GCs are offset towards higher metallicities for given stellar masses. The difference between the mass-metallicity distributions of UCDs and GCs may be qualitatively understood as a result of their different physical sizes at birth in a self-enrichment scenario or of galactic nuclear cluster star formation efficiency being relatively low in a tidal stripping scenario for UCD formation. The existing observations provide the necessary but not sufficient evidence for tidally stripped dE nuclei being the dominant contributors to the M87 UCDs.