35 research outputs found
Hi-line mapping of large-scale structures in the zone of avoidance
Includes abstract.Includes bibliographical references.This dissertation presents a survey made in the 21 cm wavelength line of the neutral hydrogen (HI) to determine redshifts of 928 galaxy candidates in the Zone of Avoidance (ZoA). The 2MASS Redshift Survey (2MRS) is currently the most uniform “whole-sky" redshift survey for mapping large-scale structures, and studying the dynamics in the nearby Universe and the Cosmic Microwave Background (CMB) dipole. While this survey is supposed to cover the whole sky, it excludes the inner ZoA because of difficulties in detecting galaxies due to the heavy obscuration caused by dust and stellar crowding. The lack of redshift data in the ZoA remains the main source of uncertainties in studies of the nearby Universe. To improve on this, the 100m-class Nançay Radio Telescope was used to measure the 21 cm line emission of 928 near-infrared bright galaxy candidates without redshift information in the ZoA which are accessible from the NRT (Dec > -39°), hence focuses predominantly on the mostly unexplored northern ZoA
The evolution of the cold gas fraction in nearby clusters ram-pressure stripped galaxies
Cluster galaxies are affected by the surrounding environment, which
influences, in particular, their gas, stellar content and morphology. In
particular, the ram-pressure exerted by the intracluster medium promotes the
formation of multi-phase tails of stripped gas detectable both at optical
wavelengths and in the sub-mm and radio regimes, tracing the cold molecular and
atomic gas components, respectively. In this work we analyze a sample of
sixteen galaxies belonging to clusters at redshift showing evidence
of an asymmetric HI morphology (based on MeerKAT observations) with and without
a star forming tail. To this sample we add three galaxies with evidence of a
star forming tail and no HI detection. Here we present the galaxies
gas content from APEX observations of the CO(2-1) emission. We find that in
most galaxies with a star forming tail the global content is
enhanced with respect to undisturbed field galaxies with similar stellar
masses, suggesting an evolutionary path driven by the ram-pressure stripping.
As galaxies enter into the clusters their HI is displaced but also partially
converted into , so that they are enriched when they
pass close to the pericenter, i. e. when they develop the star forming tails
that are visible in UV/B broad bands and in H emission. An inspection
of the phase-space diagram for our sample suggests an anticorrelation between
the HI and gas phases as galaxies fall into the cluster potential.
This peculiar behaviour is a key signature of the ram-pressure stripping in
action.Comment: 19 pages, 8 figures, accepted for publication in Ap
GASP XXV:Neutral hydrogen gas in the striking jellyfish galaxy JO204
We present JVLA-C observations of the HI gas in JO204, one of the most
striking jellyfish galaxies from the GASP survey. JO204 is a massive galaxy in
the low-mass cluster Abell 957 at z=0.04243. The HI map reveals an extended 90
kpc long ram-pressure stripped tail of neutral gas, stretching beyond the 30
kpc long ionized gas tail and pointing away from the cluster center. The HI
mass seen in emission is (1.32 , mostly
located in the tail. The northern part of the galaxy disk has retained some HI
gas, while the southern part has already been completely stripped and displaced
into an extended unilateral tail. Comparing the distribution and kinematics of
the neutral and ionized gas in the tail indicates a highly turbulent medium.
Moreover, we observe associated HI absorption against the 11 mJy central radio
continuum source with an estimated HI absorption column density of 3.2 cm. The absorption profile is significantly asymmetric with a
wing towards higher velocities. We modelled the HI absorption by assuming that
the HI and ionized gas disks have the same kinematics in front of the central
continuum source, and deduced a wider absorption profile than observed. The
observed asymmetric absorption profile can therefore be explained by a clumpy,
rotating HI gas disk seen partially in front of the central continuum source,
or by ram-pressure pushing the neutral gas towards the center of the continuum
source, triggering the AGN activity.Comment: 16 pages, 10 figures, accepted for publication in MNRA
The role of environment on quenching, star formation and AGN activity
Galaxies undergoing ram pressure stripping in clusters are an excellent
opportunity to study the effects of environment on both the AGN and the star
formation activity. We report here on the most recent results from the GASP
survey. We discuss the AGN-ram pressure stripping connection and some evidence
for AGN feedback in stripped galaxies. We then focus on the star formation
activity, both in the disks and the tails of these galaxies, and conclude
drawing a picture of the relation between multi-phase gas and star formation.Comment: Proceedings of the IAU Symposium 359 "Galaxy evolution and feedback
across different environments", editors T. Storchi-Bergmann, R. Overzier, W.
Forman & R. Riffel - final versio
AGN feeding and feedback in fornax a : kinematical analysis of the multi-phase ISM
We present a multi-wavelength study of the gaseous medium surrounding the nearby active galactic nucleus (AGN), Fornax A. Using MeerKAT, ALMA, and MUSE observations, we reveal a complex distribution of the atomic (H i), molecular (CO), and ionised gas in its centre and along the radio jets. By studying the multi-scale kinematics of the multi-phase gas, we reveal the presence of concurrent AGN feeding and feedback phenomena. Several clouds and an extended 3 kpc filament – perpendicular to the radio jets and the inner disk (r . 4:5 kpc) – show highly-turbulent kinematics, which likely induces non-linear condensation and subsequent chaotic cold accretion (CCA) onto the AGN. In the wake of the radio jets and in an external (r & 4:5 kpc) ring, we identify an entrained massive ( 107 M ) multi-phase outflow (vOUT 2000 km s1). The rapid flickering of the nuclear activity of Fornax A ( 3 Myr) and the gas experiencing turbulent condensation raining onto the AGN provide quantitative evidence that a recurrent, tight feeding and feedback cycle may be self-regulating the activity of Fornax A, in agreement with CCA simulations. To date, this is one of the most in-depth probes of such a mechanism, paving the way to apply these precise diagnostics to a larger sample of nearby AGN hosts and their multi-phase inter stellar medium.The European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme; Montage is funded by the National Science Foundation; the Department of Science and Technology and National Research Foundation.http://www.hanspub.org/Journal/AAS.htmlam2022Physic
MeerKAT-16 H I observation of the dIrr galaxy WLM
We present observations and models of the kinematics and the distribution of
the neutral hydrogen (HI) in the isolated dwarf irregular galaxy,
Wolf-Lundmark-Melotte (WLM). We observed WLM with the Green Bank Telescope
(GBT) and as part of the MeerKAT Early Science Programme, where 16 dishes were
available. The HI disc of WLM extends out to a major axis diameter of 30 arcmin
(8.5 kpc), and a minor axis diameter of 20 arcmin (5.6 kpc) as measured by the
GBT. We use the MeerKAT data to model WLM using the TiRiFiC software suite,
allowing us to fit different tilted-ring models and select the one that best
matches the observation. Our final best-fitting model is a flat disc with a
vertical thickness, a constant inclination and dispersion, and a
radially-varying surface brightness with harmonic distortions. To simulate
bar-like motions, we include second-order harmonic distortions in velocity in
the tangential and the vertical directions. We present a model with only
circular motions included and a model with non-circular motions. The latter
describes the data better. Overall, the models reproduce the global
distribution and the kinematics of the gas, except for some faint emission at
the 2-sigma level. We model the mass distribution of WLM with a
pseudo-isothermal (ISO) and a Navarro-Frenk-White (NFW) dark matter halo
models. The NFW and the ISO models fit the derived rotation curves within the
formal errors, but with the ISO model giving better reduced chi-square values.
The mass distribution in WLM is dominated by dark matter at all radii.Comment: Accepted for publication in MNRAS, 25 pages, 21 figures, 5 table
Collimated synchrotron threads linking the radio lobes of ESO 137-006
We present MeerKAT 1000 MHz and 1400 MHz observations of a bright radio galaxy in the southern hemisphere, ESO 137-006. The
galaxy lies at the centre of the massive and merging Norma galaxy cluster. The MeerKAT continuum images (rms ∼0.02 mJy beam−1
at ∼1000 resolution) reveal new features that have never been seen in a radio galaxy before: collimated synchrotron threads of yet
unknown origin, which link the extended and bent radio lobes of ESO 137-006. The most prominent of these threads stretches in
projection for about 80 kpc and is about 1 kpc in width. The radio spectrum of the threads is steep, with a spectral index of up to α ' 2
between 1000 and 1400 MHz.http://www.aanda.orgpm2021Physic