20 research outputs found
The H I angular momentum-mass relation
We study the relationship between the H I specific angular momentum () and the H I mass () for a sample of galaxies with well-measured H I rotation curves. We find that the relation is well described by an unbroken power law ∝ α over the entire mass range (107-1010.5 M⊙), with α = 0.89 ± 0.05 (scatter 0.18 dex). This is in reasonable agreement with models which assume that evolutionary processes maintain H I discs in a marginally stable state. The slope we observe is also significantly different from both the j ∝ M2/3 relation expected for dark matter haloes from tidal torquing models and the observed slope of the specific angular momentum-mass relation for the stellar component of disc galaxies. Our sample includes two H I-bearing ultra-diffuse galaxies, and we find that their angular momentum follows the same relation as other galaxies. The only discrepant galaxies in our sample are early-type galaxies with large rotating H I discs, which are found to have significantly higher angular momentum than expected from the power-law relation. The H I discs of all these early-type galaxies are misaligned or counter-rotating with respect to the stellar discs, consistent with the gas being recently accreted. We speculate that late-stage wet mergers, as well as cold flows play a dominant role in determining the kinematics of the baryonic component of galaxies as suggested by recent numerical simulations
Probing galaxy evolution through HI 21-cm emission and absorption: current status and prospects with the Square Kilometre Array
One of the major science goals of the Square Kilometre Array (SKA) is to
understand the role played by atomic hydrogen (HI) gas in the evolution of
galaxies throughout cosmic time. The hyperfine transition line of the hydrogen
atom at 21-cm is one of the best tools to detect and study the properties of HI
gas associated with galaxies. In this article, we review our current
understanding of HI gas and its relationship with galaxies through observations
of the 21-cm line both in emission and absorption. In addition, we provide an
overview of the HI science that will be possible with SKA and its pre-cursors
and pathfinders, i.e. HI 21-cm emission and absorption studies of galaxies from
nearby to high redshifts that will trace various processes governing galaxy
evolution.Comment: 31 pages, 7 figures, accepted on 27 May 2022 for publication in the
Journal of Astrophysics and Astronomy (to appear in the special issue on
"Indian participation in the SKA"), figure 4 has been update
MIGHTEE-HI: the HI Size-Mass relation over the last billion years
We present the observed HI size-mass relation of galaxies from the
MIGHTEE Survey Early Science data. The high sensitivity of MeerKAT allows us to
detect galaxies spanning more than 4 orders of magnitude in HI mass, ranging
from dwarf galaxies to massive spirals, and including all morphological types.
This is the first time the relation has been explored on a blind homogeneous
data set which extends over a previously unexplored redshift range of , i.e. a period of around one billion years in cosmic time. The sample
follows the same tight logarithmic relation derived from previous work, between
the diameter () and the mass () of HI discs. We measure
a slope of , an intercept of , and an
observed scatter of dex. For the first time, we quantify the intrinsic
scatter of dex (), which provides a constraint
for cosmological simulations of galaxy formation and evolution. We derive the
relation as a function of galaxy type and find that their intrinsic scatters
and slopes are consistent within the errors. We also calculate the relation for two redshift bins and do not find any evidence for
evolution with redshift. These results suggest that over a period of one
billion years in lookback time, galaxy discs have not undergone significant
evolution in their gas distribution and mean surface mass density, indicating a
lack of dependence on both morphological type and redshift.Comment: 10 pages, 5 figures, accepted for publication in MNRA
MIGHTEE-HI: The first MeerKAT HI mass function from an untargeted interferometric survey
We present the first measurement of the HI mass function (HIMF) using data
from MeerKAT, based on 276 direct detections from the MIGHTEE Survey Early
Science data covering a period of approximately a billion years (). This is the first HIMF measured using interferometric data over
non-group or cluster field, i.e. a deep blank field. We constrain the
parameters of the Schechter function which describes the HIMF with two
different methods: and Modified Maximum Likelihood (MML).
We find a low-mass slope , `knee' mass
and normalisation
(
kms Mpc) for and
, `knee' mass and normalisation for MML. When using we
find both the low-mass slope and `knee' mass to be consistent within
with previous studies based on single-dish surveys. The cosmological mass
density of HI is found to be slightly larger than previously reported:
from and from MML but consistent within the uncertainties. We find
no evidence for evolution of the HIMF over the last billion years.Comment: 13 pages, 9 figures, accepted for publication in MNRA
MIGHTEE-HI: HI galaxy properties in the large scale structure environment at z ∼ 0.37 from a stacking experiment
We present the first measurement of HI mass of star-forming galaxies in different large scale structure environments from a blind survey at z ∼ 0.37. In particular, we carry out a spectral line stacking analysis considering 2875 spectra of colour-selected star-forming galaxies undetected in HI at 0.23 < z < 0.49 in the COSMOS field, extracted from the MIGHTEE-HI Early Science datacubes, acquired with the MeerKAT radio telescope. We stack galaxies belonging to different subsamples depending on three different definitions of large scale structure environment: local galaxy overdensity, position inside the host dark matter halo (central, satellite, or isolated), and cosmic web type (field, filament, or knot). We first stack the full star-forming galaxy sample and find a robust HI detection yielding an average galaxy HI mass of MHI = (8.12 ± 0.75) × 109 M⊙ at ∼11.8σ. Next, we investigate the different subsamples finding a negligible difference in MHI as a function of the galaxy overdensity. We report an HI excess compared to the full sample in satellite galaxies (MHI = (11.31 ± 1.22) × 109, at ∼10.2σ) and in filaments (MHI = (11.62 ± 0.90) × 109. Conversely, we report non-detections for the central and knot galaxies subsamples, which appear to be HI-deficient. We find the same qualitative results also when stacking in units of HI fraction (fHI). We conclude that the HI amount in star-forming galaxies at the studied redshifts correlates with the large scale structure environment
MIGHTEE-\HI: Possible interactions with the galaxy NGC~895
The transformation and evolution of a galaxy is strongly influenced by
interactions with its environment. Neutral hydrogen (\HI) is an excellent way
to trace these interactions. Here, we present \HI\ observations of the spiral
galaxy NGC~895, which was previously thought to be isolated. High-sensitivity
\HI\ observations from the MeerKAT large survey project MIGHTEE reveal possible
interaction features, such as extended spiral arms, and the two newly
discovered \HI\ companions, that drive us to change the narrative that it is an
isolated galaxy. We combine these observations with deep optical images from
the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and
its companions. We do find an excess of light in the outer parts of the
companion galaxy MGTHJ022138.1-052631 which could be an indication of
external perturbation and thus possible sign of interactions. Our analysis
shows that NGC~895 is an actively star-forming galaxy with a SFR of
, a value typical for high stellar mass
galaxies on the star forming main sequence. It is reasonable to state that
different mechanisms may have contributed to the observed features in NGC~895
and this emphasizes the need to revisit the target with more detailed
observations. Our work shows the high potential and synergy of using
state-of-the-art data in both \HI\ and optical to reveal a more complete
picture of galaxy environments.Comment: 14 pages, 10 figures. Accepted for publication in MNRA