We make a direct comparison of the derived dark matter (DM) distributions between hydrodynamical simulations of dwarf galaxies assuming a Delta *LCDM cosmology and the observed dwarf galaxies sample ...from the THINGS survey in terms of (1) the rotation curve shape and (2) the logarithmic inner density slope Delta *a of mass density profiles. The simulations, which include the effect of baryonic feedback processes, such as gas cooling, star formation, cosmic UV background heating, and most importantly, physically motivated gas outflows driven by supernovae, form bulgeless galaxies with DM cores. We show that the stellar and baryonic mass is similar to that inferred from photometric and kinematic methods for galaxies of similar circular velocity. Analyzing the simulations in exactly the same way as the observational sample allows us to address directly the so-called cusp/core problem in the Delta *LCDM model. We show that the rotation curves of the simulated dwarf galaxies rise less steeply than cold dark matter rotation curves and are consistent with those of the THINGS dwarf galaxies. The mean value of the logarithmic inner density slopes Delta *a of the simulated galaxies' DM density profiles is ~--0.4 ? 0.1, which shows good agreement with Delta *a = --0.29 ? 0.07 of the THINGS dwarf galaxies. The effect of non-circular motions is not significant enough to affect the results. This confirms that the baryonic feedback processes included in the simulations are efficiently able to make the initial cusps with Delta *a ~--1.0 to --1.5 predicted by DM-only simulations shallower and induce DM halos with a central mass distribution similar to that observed in nearby dwarf galaxies.
ABSTRACT 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 m 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 of their DM density profiles. The mean value of the slopes of the 26 LITTLE THINGS dwarf galaxies is which is in accordance with the previous results found for low surface brightness galaxies ( ) as well as the seven THINGS dwarf galaxies ( ). 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.
Abstract
We perform a profile analysis of the combined H
i
data cube of the Large Magellanic Cloud (LMC) from observations with the Australia Telescope Compact Array and the Parkes radio telescope. ...For the profile analysis, we use a newly developed algorithm that decomposes individual line profiles into an optimal number of Gaussian components based on a Bayesian nested sampling. The decomposed Gaussian components are then classified into
kinematically
cold, warm, and hot gas components based on their velocity dispersion. The estimated masses of the kinematically cold, warm, and hot gas components are ∼12.2%, ∼58.3%, and ∼29.5% of the total H
i
mass of the LMC, respectively. Our analysis reveals the highly complex H
i
structure and kinematics of the LMC that are seen in previous studies but in a more quantitative manner. We also extract the undisturbed H
i
gas bulk motions and derive new H
i
gas bulk rotation curves of the LMC by applying a 2D tilted-ring analysis. In contrast to previously derived H
i
rotation curves, the newly derived bulk rotation curves are much more consistent with the carbon star kinematics, with rotation velocity linearly increasing in the inner part and reaching a maximum of ∼60 km s
−1
at the outermost measured radius. By comparing the lower bulk rotation curves with previous studies, we conclude that there is a lower dynamical contribution of dark matter in the central part of the LMC.
ABSTRACT We present measurements of baryonic mass and specific angular momentum (sAM) in 14 rotating dwarf Irregular (dIrr) galaxies from the LITTLE THINGS sample. These measurements, based on 21 cm ...kinematic data from the Very Large Array and stellar mass maps from the Spitzer Space Telescope, extend previous AM measurements by more than two orders of magnitude in . The dwarf galaxies show systematically higher values than expected from the scaling of spiral galaxies, representative of a scale-free galaxy formation scenario. This offset can be explained by decreasing baryon mass fractions (where is the dynamical mass) with decreasing (for ). We find that the sAM of neutral atomic hydrogen (H i) alone is about 2.5 times higher than that of the stars. The M-j relation of H i is significantly steeper than that of the stars, as a direct consequence of the systematic variation of the H i fraction with .
Abstract
We present a novel algorithm that is based on a Bayesian Markov Chain Monte Carlo (MCMC) technique for performing robust profile analysis of a data cube from either single-dish or ...interferometric radio telescopes. It fits a set of models comprised of a number of Gaussian components given by the user to individual line-of-sight velocity profiles, then compares them and finds an optimal model based on the Bayesian Inference Criteria computed for each model. The decomposed Gaussian components are then classified into bulk or non-circular motions as well as kinematically cold or warm components. The fitting based on the Bayesian MCMC technique is insensitive to initial estimates of the parameters, and suffers less from finding the global minimum in models given enough sampling points and a wide range of priors for the parameters. It is found to provide reliable profile decomposition and classification of the decomposed components in a fully automated way, together with robust error estimation of the parameters as shown by performance tests using artificial data cubes. We apply the newly developed algorithm to the H i data cubes of sample galaxies from the Local Volume H i galaxy Survey (LVHIS). We also compare the kinematically cold and warm components, and bulk velocity fields with previous analyses made in a classical method.
We present mass models for the dark matter component of seven dwarf galaxies taken from 'The H I Nearby Galaxy Survey' (THINGS) and compare these with those taken from numerical Delta *L cold dark ...matter ( Delta *LCDM) simulations. The THINGS high-resolution data significantly reduce observational uncertainties and thus allow us to derive accurate dark matter distributions in these systems. We here use the bulk velocity fields when deriving the rotation curves of the galaxies. Compared to other types of velocity fields, the bulk velocity field minimizes the effect of small-scale random motions more effectively and traces the underlying kinematics of a galaxy more properly. The 'Spitzer Infrared Nearby Galaxies Survey' 3.6 Delta *mm and ancillary optical data are used for separating the baryons from their total matter content in the galaxies. The sample dwarf galaxies are found to be dark matter dominated over most radii. The relation between total baryonic (stars + gas) mass and maximum rotation velocity of the galaxies is roughly consistent with the baryonic Tully-Fisher relation calibrated from a larger sample of gas-dominated low-mass galaxies. We find discrepancies between the derived dark matter distributions of the galaxies and those of Delta *LCDM simulations, even after corrections for non-circular motions have been applied. The observed solid body-like rotation curves of the galaxies rise too slowly to reflect the cusp-like dark matter distribution in cold dark matter halos. Instead, they are better described by core-like models such as pseudo-isothermal halo models dominated by a central constant-density core. The mean value of the logarithmic inner slopes of the mass density profiles is Delta *a = --0.29 ? 0.07. They are significantly different from the steep slope of ~ -- 1.0 inferred from previous dark-matter-only simulations, and are more consistent with shallower slopes found in recent Delta *LCDM simulations of dwarf galaxies in which the effects of baryonic feedback processes are included.
LITTLE THINGS Hunter, Deidre A; FICUT-VICAS, DANA; Ashley, Trisha ...
The Astronomical journal,
11/2012, Volume:
144, Issue:
5
Journal Article
Peer reviewed
Open access
We present LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The HI Nearby Galaxy Survey), which is aimed at determining what drives star formation in dwarf galaxies. This is a ...multi-wavelength survey of 37 dwarf irregular and 4 blue compact dwarf galaxies that is centered around HI-line data obtained with the National Radio Astronomy Observatory (NRAO) Very Large Array (VLA). The HI-line data are characterized by high sensitivity (< or =, slant1.1 mJy beam super(-1) per channel), high spectral resolution (< or =, slant2.6 km s super(-1)), and high angular resolution (~6"). The LITTLE THINGS sample contains dwarf galaxies that are relatively nearby (< or =, slant 10.3 Mpc; 6" is < or =, slant 300 pc), that were known to contain atomic hydrogen, the fuel for star formation, and that cover a large range in dwarf galactic properties. We describe our VLA data acquisition, calibration, and mapping procedures, as well as HI map characteristics, and show channel maps, moment maps, velocity-flux profiles, and surface gas density profiles. In addition to the HI data we have GALEX UV and ground-based UBV and H alpha images for most of the galaxies, and JHK images for some. Spitzer mid-IR images are available for many of the galaxies as well. These data sets are available online.
Abstract
We present H
i
gas kinematics and star formation activities of NGC 6822, a dwarf galaxy located in the Local Group at a distance of ∼490 kpc. We perform profile decomposition of ...line-of-sight velocity profiles of the H
i
data cube (42.4″ × 12.0″ spatial, corresponding to ∼100 pc; 1.6 km s
−1
spectral) taken with the Australia Telescope Compact Array. For this, we use a new tool, the so-called
baygaud
, which is based on Bayesian analysis techniques, allowing us to decompose a line-of-sight velocity profile into an optimal number of Gaussian components in a quantitative manner. We classify the decomposed H
i
gas components of NGC 6822 into cool-bulk, warm-bulk, cool-non-bulk, and warm-non-bulk motions with respect to their centroid velocities and velocity dispersions. We correlate their gas surface densities with corresponding star formation rate densities derived using both the GALEX far-ultraviolet and WISE 22
μ
m data to examine the resolved Kennicutt–Schmidt (K-S) law for NGC 6822. Of the decomposed H
i
gas components, the cool-bulk component is likely to better follow the linear extension of the K-S law for molecular hydrogen (H
2
) at low gas surface densities where H
i
is not saturated.
It has long been speculated that many starburst or compact dwarf galaxies are resulted from dwarf-dwarf galaxy merging, but unequivocal evidence for this possibility has rarely been reported in the ...literature. We present the first study of deep optical broadband images of a gas-dominated blue compact dwarf galaxy (BCD) VCC 848 (M 2 × 108M ) that hosts extended stellar shells and thus is confirmed to be a dwarf-dwarf merger. VCC 848 is located in the outskirts of the Virgo Cluster. By analyzing the stellar light distribution, we found that VCC 848 is the result of a merging between two dwarf galaxies with a primary-to-secondary mass ratio 5 for the stellar components and 2 for the presumed dark matter halos. The secondary progenitor galaxy has been almost entirely disrupted. The age-mass distribution of photometrically selected star cluster candidates in VCC 848 implies that the cluster formation rate (CFR, ∝ star formation rate) was enhanced by a factor of ∼7-10 during the past ∼1 Gyr. The merging-induced enhancement of CFR peaked near the galactic center a few hundred Myr ago and has started declining in the last few tens of Myr. The current star formation activities, as traced by the youngest clusters, mainly occur at large galactocentric distances ( 1 kpc). The fact that VCC 848 is still (atomic) gas-dominated after the period of the most violent collision suggests that gas-rich dwarf galaxy merging can result in BCD-like remnants with extended atomic gas distribution surrounding a blue compact center, in general agreement with previous numerical simulations.
Abstract
The stellar, gaseous and young stellar disks in the LITTLE THINGS sample of nearby dwarf irregular galaxies are fitted with functions to search for correlations between the parameters. We ...find that the H
i
radial profiles are generally flatter in the center and fall faster in the outer regions than the
V
-band profiles, while young stars are more centrally concentrated, especially if the H
i
is more centrally flat. This pattern suggests that the H
i
is turning into molecules in the center, and the molecular clouds are forming stars and FUV. A model that assumes the molecular surface density is proportional to the total gas surface density to a power of 1.5 or 2, in analogy with the Kennicutt–Schmidt relation, reproduces the relationship between the ratio of the visible to the H
i
scale length and the H
i
Sérsic index. The molecular fraction is estimated as a function of radius for each galaxy by converting the FUV to a molecular surface density using conventional calibrations. The average molecular fraction inside 3
R
D
is 23% ± 17%. However, the break in the stellar surface brightness profile has no unified tracer related to star formation.
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