The article describes the approach followed by the Devasthal Time Allocation Committee to evaluate observing proposals to the Devasthal Optical Telescope (DOT) over the period 2020–2023, the results ...of the time allocation process, and some statistics of the proposals and final time allocation. It also provides some suggestions to the Aryabhatta Research Institute of Observational Sciences that aim to improve the DOT science output and the quality of observing proposals, as well as suggestions to DOT proposers to help improve their chances of obtaining DOT observing time in the future.
We report results from a Giant Metrewave Radio Telescope (GMRT) monitoring campaign of the black hole X-ray binary V404 Cygni during its 2015 June outburst. The GMRT observations were carried out at ...observing frequencies of 1280, 610, 325, and 235 MHz, and extended from June 26.89 UT (a day after the strongest radio/X-ray outburst) to July 12.93 UT. We find the low-frequency radio emission of V404 Cygni to be extremely bright and fast-decaying in the outburst phase, with an inverted spectrum below 1.5 GHz and an intermediate X-ray state. The radio emission settles to a weak, quiescent state 11 days after the outburst, with a flat radio spectrum and a soft X-ray state. Combining the GMRT measurements with flux density estimates from the literature, we identify a spectral turnover in the radio spectrum at 1.5 GHz on June 26.9 UT, indicating the presence of a synchrotron self-absorbed emitting region. We use the measured flux density at the turnover frequency with the assumption of equipartition of energy between the particles and the magnetic field to infer the jet radius ( 4.0 × 1013 cm), magnetic field ( 0.5 G), minimum total energy ( 7 × 1039 erg), and transient jet power ( 8 × 1034 erg s−1). The relatively low value of the jet power, despite V404 Cygni's high black hole spin parameter, suggests that the radio jet power does not correlate with the spin parameter.
We have used the upgraded Giant Metrewave Radio Telescope to carry out a deep (117 on-source hours) L-band observation of the Extended Groth Strip, to measure the average neutral hydrogen (H i) mass ...and median star formation rate (SFR) of star-forming galaxies, as well as the cosmic H i mass density, at 0.2 < z < 0.4. This was done by stacking the H i 21 cm emission and the rest-frame 1.4 GHz radio continuum from 445 blue star-forming galaxies with MB ≤ −17 at zmean 0.34. The stacked H i 21 cm emission signal is detected at 7 significance, implying an average H i mass of . We also stacked the rest-frame 1.4 GHz radio continuum emission of the same galaxies to obtain a median SFR of (0.54 0.06) M yr−1; this implies an atomic gas depletion timescale of ΔtH i = ( 9) Gyr, consistent with values in star-forming galaxies in the local universe. This indicates that the star formation efficiency does not change significantly over the redshift range 0-0.4. We used the detection of the stacked H i 21 cm emission signal to infer the normalized cosmic H i mass density ( H i/ c,0) in star-forming galaxies at z 0.34. Assuming the local relation between H i mass and absolute B-magnitude, we obtain H i/ c,0 = (4.81 0.75) × 10−4, implying no significant evolution in H i/ c,0 from z 0.4 to the present epoch.
ABSTRACT We report a Giant Metrewave Radio Telescope search for H i 21 cm emission from a large sample of massive star-forming galaxies at z 1.18-1.34, lying in sub-fields of the DEEP2 Redshift ...Survey. The search was carried out by co-adding ("stacking") the H i 21 cm emission spectra of 857 galaxies, after shifting each galaxy's H i 21 cm spectrum to its rest frame. We obtain the 3 upper limit SH i < 2.5 Jy on the average H i 21 cm flux density of the 857 galaxies, at a velocity resolution of 315 km s−1. This yields the 3 constraint on the average H i mass of the 857 stacked galaxies, the first direct constraint on the atomic gas mass of galaxies at z > 1. The implied limit on the average atomic gas mass fraction (relative to stars) is MGAS/M* < 0.5, comparable to the cold molecular gas mass fraction in similar star-forming galaxies at these redshifts. We find that the cosmological mass density of neutral atomic gas in massive star-forming galaxies at z 1.3 is GAS < 3.7 × 10−4, significantly lower than GAS estimates in both galaxies in the local universe and damped Ly absorbers at z ≥ 2.2. Massive blue star-forming galaxies thus do not appear to dominate the neutral atomic gas content of the universe at z 1.3.
Abstract
We report Giant Metrewave Radio Telescope H i 21 cm imaging of CGCG 137–068, the host galaxy of the fast-evolving luminous transient (FELT) AT2018cow. This is the first study of the gas ...properties of a FELT host galaxy. We obtain a total H i mass of (6.6 ± 0.9) × 108 M⊙ for the host galaxy, which implies an atomic gas depletion time of 3 Gyr and a gas-to-stellar mass ratio of 0.47, consistent with values in normal star-forming dwarf galaxies. At spatial resolutions of ≥6 kpc, the H i of CGCG 137–068 appears to be distributed in a disc, in mostly regular rotation. However, at spatial resolutions of 2 kpc, the highest column density H i is found to lie in an asymmetric ring around the central regions, with H i column densities ≥1021 cm−2; AT2018cow lies within this high column density ring. This H i ring could be suggestive of an interaction between CGCG 137–068 and a companion galaxy. Such a ring is ideal for the formation of compact regions of star formation hosting massive stars, favouring massive star progenitor models for AT2018cow. We measure a 1.4 GHz flux density of 1.13 ± 0.13 mJy for AT2018cow on 2018 August 27.
Abstract
We report a ≈400 hr Giant Metrewave Radio Telescope (GMRT) search for H
i
21 cm emission from star-forming galaxies at
z
= 1.18–1.39 in seven fields of the DEEP2 Galaxy Survey. Including ...data from an earlier 60 hr GMRT observing run, we co-added the H
i
21 cm emission signals from 2841 blue star-forming galaxies that lie within the FWHM of the GMRT primary beam. This yielded a 5.0
σ
detection of the average H
i
21 cm signal from the 2841 galaxies at an average redshift 〈
z
〉 ≈ 1.3, only the second detection of H
i
21 cm emission at
z
≥ 1. We obtain an average H
i
mass of 〈M
HI
〉 = (3.09 ± 0.61) × 10
10
M
⊙
and an H
i
-to-stellar mass ratio of 2.6 ± 0.5, both significantly higher than values in galaxies with similar stellar masses in the local universe. We also stacked the 1.4 GHz continuum emission of the galaxies to obtain a median star formation rate (SFR) of 14.5 ± 1.1 M
⊙
yr
−1
. This implies an average H
i
depletion timescale of ≈2 Gyr for blue star-forming galaxies at
z
≈ 1.3, a factor of ≈3.5 lower than that of similar local galaxies. Our results suggest that the H
i
content of galaxies toward the end of the epoch of peak cosmic SFR density is insufficient to sustain their high SFR for more than ≈2 Gyr. Insufficient gas accretion to replenish the H
i
could then explain the observed decline in the cosmic SFR density at
z
< 1.
ABSTRACT We use the Hubble Space Telescope (HST) archive of ultraviolet (UV) quasar spectroscopy to conduct the first blind survey for damped Ly absorbers (DLAs) at low redshift ( ). Our statistical ...sample includes 463 quasars with spectral coverage spanning a total redshift path or an absorption path . Within this survey path, we identify 4 DLAs defined as absorbers with H i column density cm−2, which implies an incidence per absorption length at a median survey path redshift of z = 0.623. While our estimate of is lower than earlier estimates at from H i 21 cm emission studies, the results are consistent within the measurement uncertainties. Our data set is too small to properly sample the frequency distribution function , but the observed distribution agrees with previous estimates at . Adopting the shape of , we infer an H i mass density at of . This is significantly lower than previous estimates from targeted DLA surveys with the HST, but consistent with results from low-z H i 21 cm observations, and suggests that the neutral gas density of the universe has been decreasing over the past 10 Gyr.
Abstract
We report a Giant Metrewave Radio Telescope
21 cm mapping study of the neutral atomic hydrogen (H
i
) in the host galaxy of the fast radio burst (FRB) FRB 20180916B at
z
≈ 0.03399. We find ...that the FRB host has an H
i
mass of
M
H
i
= (2.74 ± 0.33) × 10
9
M
⊙
and a high H
i
to stellar mass ratio, ≈1.3. The FRB host is thus a gas-rich but near-quiescent galaxy that is likely to have acquired a significant mass of H
i
in the recent past. The H
i
distribution is disturbed, with extended H
i
21 cm emission detected in a northeastern tail, a counter-tail toward the south, an H
i
hole between the galaxy center and the FRB location, and a high H
i
column density measured close to the FRB position. The FRB host is part of a group with four companions detected in their H
i
21 cm emission, the nearest of which is only 22 kpc from the FRB location. The gas richness and disturbed H
i
distribution indicate that the FRB host has recently undergone a minor merger, which increased its H
i
mass, disturbed the H
i
in the galaxy disk, and compressed the H
i
near the FRB location to increase its surface density. We propose that this merger caused the burst of star formation in the outskirts of the galaxy that gave rise to the FRB progenitor. The evidence for a minor merger is consistent with scenarios in which the FRB progenitor is a massive star, formed due to the merger event.
Abstract We present the first estimate, based on direct H i 21 cm observations, of the H i mass function (H i MF) of star-forming galaxies at z ≈ 1, obtained by combining our measurement of the ...scaling relation between H i mass ( M H i ) and B -band luminosity ( M B ) of star-forming galaxies with a literature estimate of the B -band luminosity function at z ≈ 1. We determined the M H i – M B relation by using the GMRT-CAT z 1 survey of the DEEP2 fields to measure the average H i mass of blue galaxies at z = 0.74–1.45 in three separate M B subsamples. This was done by separately stacking the H i 21 cm emission signals of the galaxies in each subsample to detect, at (3.5–4.4) σ significance, the average H i 21 cm emission of each subsample. We find that the M H i – M B relation at z ≈ 1 is consistent with that at z ≈ 0. We combine our estimate of the M H i – M B relation at z ≈ 1 with the B -band luminosity function at z ≈ 1 to determine the H i MF at z ≈ 1. We find that the number density of galaxies with M H i > 10 10 M ⊙ (higher than the knee of the local H i mass function) at z ≈ 1 is a factor of ≈4–5 higher than that at z ≈ 0, for a wide range of assumed scatters in the M H i – M B relation. We rule out the hypothesis that the number density of galaxies with M H i > 10 10 M ⊙ remains unchanged between z ≈ 1 and z ≈ 0 at ≳99.7% confidence. This is the first statistically significant evidence for evolution in the H i MF of galaxies from the epoch of cosmic noon.
Abstract
We present here estimates of the average rates of accretion of neutral gas onto main-sequence galaxies and the conversion of atomic gas to molecular gas in these galaxies at two key epochs ...in galaxy evolution: (i)
z
≈ 1.3–1.0, toward the end of the epoch of peak star formation activity in the Universe, and (ii)
z
≈ 1–0, when the star formation activity declines by an order of magnitude. We determine the net gas accretion rate
R
Acc
and the molecular gas formation rate
R
Mol
by combining the relations between the stellar mass and the atomic gas mass, the molecular gas mass, and the star formation rate (SFR) at three epochs,
z
= 1.3,
z
= 1.0, and
z
= 0, with the assumption that galaxies evolve continuously on the star-forming main sequence. We find that, for all galaxies,
R
Acc
is far lower than the average SFR
R
SFR
at
z
≈ 1.3–1.0; however,
R
Mol
is similar to
R
SFR
during this interval. Conversely, both
R
Mol
and
R
Acc
are significantly lower than
R
SFR
over the later interval,
z
≈ 1–0. We find that massive main-sequence galaxies had already acquired most of their present-day baryonic mass by
z
≈ 1.3. At
z
≈ 1.3–1.0, the rapid conversion of the existing atomic gas to molecular gas was sufficient to maintain a high average SFR, despite the low net gas accretion rate. However, at later times, the combination of the lower net gas accretion rate and the lower molecular gas formation rate leads to a decline in the fuel available for star formation and results in the observed decrease in the SFR density of the Universe over the last 8 Gyr.
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