31 research outputs found
KAT-7 Science Verification: Using HI Observations of NGC 3109 to Understand its Kinematics and Mass Distribution
HI observations of the Magellanic-type spiral NGC 3109, obtained with the
seven dish Karoo Array Telescope (KAT-7), are used to analyze its mass
distribution. Our results are compared to what is obtained using VLA data.
KAT-7 is the precursor of the SKA pathfinder MeerKAT, which is under
construction. The short baselines and low system temperature of the telescope
make it sensitive to large scale low surface brightness emission. The new
observations with KAT-7 allow the measurement of the rotation curve of NGC 3109
out to 32', doubling the angular extent of existing measurements. A total HI
mass of 4.6 x 10^8 Msol is derived, 40% more than what was detected by the VLA
observations.
The observationally motivated pseudo-isothermal dark matter (DM) halo model
can reproduce very well the observed rotation curve but the cosmologically
motivated NFW DM model gives a much poorer fit to the data. While having a more
accurate gas distribution has reduced the discrepancy between the observed RC
and the MOdified Newtonian Dynamics (MOND) models, this is done at the expense
of having to use unrealistic mass-to-light ratios for the stellar disk and/or
very large values for the MOND universal constant a0. Different distances or HI
contents cannot reconcile MOND with the observed kinematics, in view of the
small errors on those two quantities. As for many slowly rotating gas-rich
galaxies studied recently, the present result for NGC 3109 continues to pose a
serious challenge to the MOND theory.Comment: 25 pages, 20 figures, accepted for publication in Astronomical
Journa
Effect of the environment on star formation activity and stellar mass for star-forming galaxies in the COSMOS field
We investigate the relationship between the environment and the galaxy main sequence (the relationship between stellar mass and star formation rate), as well as the relationship between the environment and radio luminosity (â P1.4GHzâ ), to shed new light on the effects of the environment on galaxies. We use the VLA-COSMOS 3-GHz catalogue, which consists of star-forming galaxies and quiescent galaxies (active galactic nuclei) in three different environments (field, filament, cluster) and for three different galaxy types (satellite, central, isolated). We perform for the first time a comparative analysis of the distribution of star-forming galaxies with respect to the main-sequence consensus region from the literature, taking into account galaxy environment and using radio observations at 0.1 †z †1.2
The far-infrared-radio correlation in MS0451-03
We present a multiwavelength analysis of star-forming galaxies in the massive cluster MS0451.6-0305 at z Ë 0.54 to shed new light on the evolution of the far-infrared-radio relationship in distant rich clusters. We have derived total infrared luminosities for a spectroscopically confirmed sample of cluster and field galaxies through an empirical relation based on Spitzer Multiband Imaging Photometer for Spitzer 24 ÎŒm photometry. The radio flux densities were measured from deep Very Large Array 1.4 GHz radio continuum observations. We find the ratio of far-infrared to radio luminosity for galaxies in an intermediate-redshift cluster to be qFIR = 1.80 ± 0.15 with a dispersion of 0.53. Due to the large intrinsic dispersion, we do not find any observable change in this value with either redshift or environment. However, a higher percentage of galaxies in this cluster show an excess in their radio fluxes when compared to low-redshift clusters (27^{+23}_{-13} per cent to 11 per cent), suggestive of a cluster enhancement of radio-excess sources at this earlier epoch. In addition, the far-infrared-radio relationship for blue galaxies, where qFIR = 2.01 ± 0.14 with a dispersion of 0.35, is consistent with the predicted value from the field relationship, although these results are based on a sample from a single cluster
Dark matter distribution in Milky Way-analog galaxies
Our current understanding of how dark matter (DM) is distributed within the
Milky Way (MW) halo, particularly in the solar neighborhood, is based on either
careful studies of the local stellar orbits or model assumptions on the global
shape of the MW halo. In this work, we undertake a study of external galaxies,
with the intent of providing insight to the DM distribution in MW-analog
galaxies. For this, we carefully select a sample of galaxies similar to the MW,
based on maximum atomic hydrogen (HI) rotational velocity (v=200-280 km s^{-1})
and morphological type (Sab-Sbc) criteria. With a need for deep,
highly-resolved HI, our resulting sample is composed of 5 galaxies from the
VIVA and THINGS surveys. To perform our baryonic analysis, we use deep Spitzer
mid-IR images at 3.6 and 4.5 {\mu}m from the S4G survey. Based on the dynamical
three-dimensional modeling software 3D-Barolo, we construct RCs and derive the
gas and stellar contributions from the galaxy\'s gaseous- and stellar-disks
mass surface density profiles. Through a careful decomposition of their
rotation curves into their baryonic (stars, gas) and DM components, we isolate
the DM contribution by using an MCMC-based approach. Based on the Sun\'s
location and the MW\'s R_{25}, we define the corresponding location of the
solar neighborhood in these systems. We put forward a window for the DM density
(\rho=0.21-0.46 GeV cm^{-3}) at these galactocentric distances in our MW analog
sample, consistent with the values found for the MW\'s local DM density, based
on more traditional approaches found in the literature.Comment: 16 pages, 6 figures, 3 tables, submitted to Ap
MIGHTEE: total intensity radio continuum imaging and the COSMOS / XMM-LSS Early Science fields
© 2021 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1093/mnras/stab3021MIGHTEE is a galaxy evolution survey using simultaneous radio continuum, spectro-polarimetry, and spectral line observations from the South African MeerKAT telescope. When complete, the survey will image 20 deg over the COSMOS, E-CDFS, ELAIS-S1, and XMM-LSS extragalactic deep fields with a central frequency of 1284 MHz. These were selected based on the extensive multiwavelength datasets from numerous existing and forthcoming observational campaigns. Here we describe and validate the data processing strategy for the total intensity continuum aspect of MIGHTEE, using a single deep pointing in COSMOS (1.6 deg) and a three-pointing mosaic in XMM-LSS (3.5 deg). The processing includes the correction of direction-dependent effects, and results in thermal noise levels below 2~Jy beam in both fields, limited in the central regions by classical confusion at 8 angular resolution, and meeting the survey specifications. We also produce images at 5 resolution that are 3 times shallower. The resulting image products form the basis of the Early Science continuum data release for MIGHTEE. From these images we extract catalogues containing 9,896 and 20,274 radio components in COSMOS and XMM-LSS respectively. We also process a close-packed mosaic of 14 additional pointings in COSMOS and use these in conjunction with the Early Science pointing to investigate methods for primary beam correction of broadband radio images, an analysis that is of relevance to all full-band MeerKAT continuum observations, and wide field interferometric imaging in general. A public release of the MIGHTEE Early Science continuum data products accompanies this article.Peer reviewedFinal Accepted Versio
MIGHTEE: multi-wavelength counterparts in the COSMOS field
In this paper we combine the Early Science radio continuum data from the
MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey,
with optical and near-infrared data and release the cross-matched catalogues.
The radio data used in this work covers deg of the COSMOS field,
reaches a thermal noise of Jy/beam and contains radio
components. We visually inspect and cross-match the radio sample with optical
and near-infrared data from the Hyper Suprime-Cam (HSC) and UltraVISTA surveys.
This allows the properties of active galactic nuclei and star-forming
populations of galaxies to be probed out to . Additionally, we use
the likelihood ratio method to automatically cross-match the radio and optical
catalogues and compare this to the visually cross-matched catalogue. We find
that 94 per cent of our radio source catalogue can be matched with this method,
with a reliability of per cent. We proceed to show that visual
classification will still remain an essential process for the cross-matching of
complex and extended radio sources. In the near future, the MIGHTEE survey will
be expanded in area to cover a total of 20~deg; thus the combination
of automated and visual identification will be critical. We compare redshift
distribution of SFG and AGN to the SKADS and T-RECS simulations and find more
AGN than predicted at .Comment: 15 pages, 15 figures. Accepted for publication in MNRA
MIGHTEE: Are giant radio galaxies more common than we thought?
We report the discovery of two new giant radio galaxies (GRGs) using the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey. Both GRGs were found within a âŒ1âdeg2 region inside the COSMOS field. They have redshifts of z = 0.1656 and z = 0.3363 and physical sizes of 2.4âMpc and 2.0âMpc, respectively. Only the cores of these GRGs were clearly visible in previous high resolution VLA observations, since the diffuse emission of the lobes was resolved out. However, the excellent sensitivity and uv coverage of the new MeerKAT telescope allowed this diffuse emission to be detected. The GRGs occupy an unpopulated region of radio power â size parameter space. Based on a recent estimate of the GRG number density, the probability of finding two or more GRGs with such large sizes at z < 0.4 in a âŒ1âdeg2 field is only 2.7 Ă 10â6, assuming Poisson statistics. This supports the hypothesis that the prevalence of GRGs has been significantly underestimated in the past due to limited sensitivity to low surface brightness emission. The two GRGs presented here may be the first of a new population to be revealed through surveys like MIGHTEE which provide exquisite sensitivity to diffuse, extended emission