4 research outputs found
Witnessing the star-formation quenching in ellipticals
We study the evolution of elliptical galaxies in the color-magnitude
diagram in terms of their star-formation history and environment, in an attempt
to learn about their quenching process. We have visually extracted 1109
galaxies from a sample of 36500 galaxies that were spectroscopically selected
from Stripe82 of the Sloan Digital Sky Survey. From this sample we have
selected 51 ellipticals based on their surface-brightness profile being
well-fitted by a single Srsic profile with Srsic indices
. Our sample consists of 12 blue-cloud ellipticals (BLE), 11
green-valley ellipticals (GLE), and 28 red-sequence ellipticals
(RLE). We find that most of the RLEs and GLEs have been quenched only recently,
or are still forming stars, based on their [{O\sc{iii}}] and H
emission, while the BLEs are forming stars vigorously. The star-formation in
BLEs is found to be extended over the galaxy and not confined to their central
region. In about 40\% of the ellipticals (ten BLEs, four GLEs and five
RLEs), star-formation quenching seems to have started only recently, based on
the lower [{O\sc{iii}}] emission compared to the [{O\sc{ii}}] and H
emission, at a given metallicity. We also find that the galaxy color is
correlated with the cosmic-web environment, with the BLEs tending to reside in
lower-density regions, the RLEs preferring denser, clustered regions, and the
GLEs found in either. One possible scenario is that as the star-forming
ellipticals migrate into the clusters, their star formation is suffocated by
the hot intra-cluster medium.Comment: Accepted for publication in MNRA
Lyman Continuum Leakers in the AstroSat Ultraviolet Deep Field: Extreme-ultraviolet Emitters at the Cosmic Noon
We report the direct detection of Lyman continuum (LyC) emission from nine galaxies and one active galactic nucleus at z ∼ 1.1–1.6 in the GOODS-North field using deep observations from the Ultraviolet Imaging Telescope (UVIT) on board AstroSat. The absolute escape fraction of the sources estimated from the far-ultraviolet and H α -line luminosities using Monte Carlo analysis of two intergalactic medium models span a range ∼10%–55%. The rest-frame UV wavelength of the sources falls in the extreme-ultraviolet regime ∼550–700 Å, the shortest LyC wavelength range probed so far. This redshift range remains devoid of direct detections of LyC emission due to the instrumental limitations of previously available facilities. With UVIT having very low detector noise, each of these sources is detected with an individual signal-to-noise ratio (S/N) > 3, while for the stack of six sources, we achieve an S/N ∼ 7.4. The LyC emission is seen to be offset from the optical centroids and extended beyond the UVIT point-spread function of 1.″6 in most of the sources. This sample fills an important niche between GALEX and Cosmic Origins Spectrograph at low z and Hubble Space Telescope's Wide Field Camera 3 at high z and is crucial in understanding the evolution of LyC leakers