601 research outputs found
The OH Megamaser Emission in Arp\,220: the rest of the story
The OH Megamaser emission in the merging galaxy Arp220 has been re-observed
with the Multi-Element Radio Linked Interferometer Network (MERLIN) and the
European VLBI Network (EVN). Imaging results of the OH line emission at the two
nuclei are found to be consistent with earlier observations and confirm
additional extended emission structures surrounding the nuclei. Detailed
information about the distributed emission components around the two nuclei has
been obtained using a concatenated MERLIN and EVN database with intermediate
(40 mas) spatial resolution. Continuum imaging shows a relatively compact West
nucleus and a more extended East nucleus in addition to an extended continuum
ridge stretching below and beyond the two nuclei. Spectral line imaging show
extended emission regions at both nuclei together with compact components and
additional weaker components north and south of the West nucleus. Spectral line
analysis indicates that the dominant OH line emission originates in foreground
molecular material that is part of a large-scale molecular structure that
engulfs the whole nuclear region. Compact OH components are representative of
star formation regions within the two nearly edge-on nuclei and define the
systemic velocities of East and West as 5425 km/s and 5360 km/s.
The foreground material at East and West has a 100 km/s lower velocity at
5314 and 5254 km/s. These emission results confirm a maser amplification
scenario where the background continuum and the line emission of the star
formation regions are amplified by foreground masering material that is excited
by the FIR radiation field originating in the two nuclear regions.Comment: 17 pages, 18 figure
FAST discovery of a fast neutral hydrogen outflow
In this letter, we report the discovery of a fast neutral hydrogen outflow in
SDSS J145239.38+062738.0, a merging radio galaxy containing an optical type I
active galactic nuclei (AGN). This discovery was made through observations
conducted by the Five-hundred-meter Aperture Spherical radio Telescope (FAST)
using redshifted 21-cm absorption. The outflow exhibits a blueshifted velocity
likely up to with respect to the systemic velocity
of the host galaxy with an absorption strength of corresponding to an optical depth of 0.002 at . The mass outflow rate ranges between and , implying an energy outflow rate ranging between
and , assuming 100 K
1000 K. Plausible drivers of the outflow include the star bursts,
the AGN radiation, and the radio jet, the last of which is considered the most
likely culprit according to the kinematics. By analysing the properties of the
outflow, the AGN, and the jet, we find that if the HI outflow is driven by the
AGN radiation, the AGN radiation seems not powerful enough to provide negative
feedback whereas the radio jet shows the potential to provide negative
feedback. Our observations contribute another example of a fast outflow
detected in neutral hydrogen, as well as demonstrate the capability of FAST in
detecting such outflows.Comment: Accepted by ApJ
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
Does a radio jet drive the massive multi-phase outflow in the ultra-luminous infrared galaxy IRAS 10565+2448?
We present new upgraded Giant Metrewave Radio Telescope (uGMRT) HI 21-cm
observations of the ultra-luminous infrared galaxy IRAS 10565+2448, previously
reported to show blueshifted, broad, and shallow HI absorption indicating an
outflow. Our higher spatial resolution observations have localised this
blueshifted outflow, which is 1.36 kpc southwest of the radio centre and
has a blueshifted velocity of and a full width at
half maximum (FWHM) of . The spatial extent and
kinematic properties of the HI outflow are consistent with the previously
detected cold molecular outflows in IRAS 10565+2448, suggesting that they
likely have the same driving mechanism and are tracing the same outflow. By
combining the multi-phase gas observations, we estimate a total outflowing mass
rate of at least and a total energy loss rate of
at least , where the contribution from the
ionised outflow is negligible, emphasising the importance of including both
cold neutral and molecular gas when quantifying the impact of outflows. We
present evidence of the presence of a radio jet and argue that this may play a
role in driving the observed outflows. The modest radio luminosity
of the jet in IRAS
10565+2448 implies that the jet contribution to driving outflows should not be
ignored in low radio luminosity AGN.Comment: 12 pages, 9 figures, accepted for publication in MNRA
- …