10 research outputs found
Rejuvenating Star Formation Activity in an Early-type Dwarf Galaxy, LEDA 1915372, with Accreted HI Gas
We report a rare astrophysical phenomenon, in which an early-type dwarf
galaxy (dE), LEDA 1915372, is accreting gas from a nearby star-forming dwarf
galaxy, MRK 0689, and is rejuvenating star-formation activity at the center.
Both LEDA 1915372 and MRK 0689 have similar brightness of = 16.99
and 16.78 mag, respectively. They are located in a small group environment,
separated by a sky-projected distance of 20.27 kpc (up to 70 kpc in three
dimension), and have a relative line-of-sight radial velocity of 6 km/s. The
observation of 21 cm emission with the Giant Metrewave Radio Telescope provides
strong evidence of interaction between the pair dwarf galaxies in terms of
neutral hydrogen (HI) morphology and kinematics. In particular, the HI map
reveals that the two galaxies are clearly connected by a gas bridge, and the
gas components of both LEDA 1915372 and MRK 0689 share a common direction of
rotation. We also find that the HI emission peak deviates from LEDA 1915372
toward its optical blue plume, suggesting a tidal origin of ongoing central
star formation. Our findings provide a new path to the formation of blue-cored
dEs.Comment: Accepted for publication in 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
The Low-redshift Lyman Continuum Survey: Radio continuum properties of low- Lyman continuum emitters
The sources that leak Lyman-continuum (LyC) photons and lead to the
reionisation of the universe are intensely studied using multiple observing
facilities. Recently, the Low-redshift LyC Survey (LzLCS) has found the first
large sample of LyC emitting galaxies at low redshift () with the
Hubble Space Telescope/Cosmic Origins Spectrograph. The LzLCS sample contains a
robust estimate of the LyC escape fraction () for
66 galaxies spanning a wide range of . Here we,
for the first time, aim to study the radio continuum (RC) properties of LzLCS
sources and their dependence on . We present Karl
G. Jansky Very Large Array RC observations at C (4-8 GHz), S (2-4 GHz) and L
(1-2 GHz) bands for a sub-sample of the LzLCS sources. The radio spectral index
() spans a wide range from being flat (
) to very steep (). We find that the strongest leakers in
our sample show flat , weak leakers have
close to normal star-forming galaxies,
and non-leakers are characterized by steep
. We argue that a combination of young
ages, free-free absorption, and a flat cosmic-ray energy spectrum can
altogether lead to a flat for strong
leakers. Non-leakers are characterized by steep spectra which can arise due to
break/cutoff at high frequencies. Such a cutoff in the spectrum can arise in a
single injection model of CRs characteristic of galaxies which have recently
stopped star formation. Such a relation between
and hints
at the interesting role of supernovae, CRs, and magnetic fields in facilitating
the escape (and/or the lack) of LyC photons.Comment: 25 pages, 14 figures, 3 tables, Submitted to Astronomy & Astrophysic
Discovery of a large H i ring around the quiescent galaxy AGC 203001
International audienceHere we report the discovery with the Giant Metrewave Radio Telescope of an extremely large (˜115 kpc in diameter) H I ring, located around a massive quenched galaxy, AGC 203001, but off-centered, with respect to it. This ring does not have any bright extended optical counterpart unlike several other known ring galaxies. Our deep g, r, and i optical imaging of the H I ring, using the MegaCam instrument on the Canada-France-Hawaii Telescope, shows however several regions with faint optical emission at a surface brightness level of ˜28 mag/arcsec2. Such an extended H I structure is very rare with only one other case known so far - the Leo ring. Conventionally, off-centered rings have been explained by a collision with an "intruder" galaxy leading to expanding density waves of gas and stars in the form of a ring. However, in such a scenario the impact also leads to large amounts of star formation in the ring which is not observed in the ring presented in this paper. We discuss possible scenarios for the formation of such H I dominated rings