High-resolution Mass Models of Dwarf Galaxies from LITTLE THINGS
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 which is a = -.032 ± 0.24 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.
© 2015. The American Astronomical Society. Received 2014 November 14; accepted 2015 February 3; published 2015 May 12. We thank W. J. G. de Blok for providing the inner density slopes and stellar masses of the THINGS disk galaxies and useful comments and discussion. We thank Fabio Governato, Andrew Pontzen, Chris Brook and Arianna Di Cintio for useful discussion on the simulations and providing the data. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. This work was funded in part by the National Science Foundation through grants AST-0707563 and AST-0707426 to D. A. H. and B. G. E.
Published - 1538-3881_149_6_180.pdf
Submitted - 1502.01281v1.pdf