Jayaram N. Chengalur

National Centre for Radio Astrophysics

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Nissim Kanekar

National Centre for Radio Astrophysics

Ayesha Begum

Baylor University

ИД

И. Д. Караченцев

Special Astrophysical Observatory

Somnath Bharadwaj

Indian Institute of Technology Kharagpur

Aditya Chowdhury

National Centre for Radio Astrophysics

Jayanta Roy

National Centre for Radio Astrophysics

S. A. Pustilnik

Special Astrophysical Observatory

Narendra Nath Patra

Indian Institute of Technology Indore

Sambit Roychowdhury

Ludwig-Maximilians-Universität München

Sanjay Kudale

National Centre for Radio Astrophysics

Cooperative Institutions

National Centre for Radio Astrophysics

Tata Institute of Fundamental Research

Astronomy and Space

Commonwealth Scientific and Industrial Research Organisation

Netherlands Institute for Radio Astronomy

National Radio Astronomy Observatory

Max Planck Society

Special Astrophysical Observatory

Centre National de la Recherche Scientifique

Cornell University

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In-field phasing at the upgraded GMRT

arXiv (Cornell University) (2024)

Sanjay Kudale Jayanta Roy Jayaram N. Chengalur Shyam Sundar Sharma Sangita Kumari

In time-domain radio astronomy with arrays, voltages from individual antennas are added together with proper delay and fringe correction to form the beam in real-time. In order to achieve the correct phased addition of antenna voltages one has to also correct for the ionospheric and instrumental gains. Conventionally this is done using observations of a calibrator source located near to the target field. This scheme is sub-optimal since it does not correct for the variation of the gains with time and position in the sky. Further, since the ionospheric phase variation is typically most rapid at the longest baselines, the most distant antennas are often excluded while forming the beam. We present here a different methodology ("in-field phasing"), in which the gains are obtained in real-time using a model of the intensity distribution in the target field, which overcomes all of these drawbacks. We present observations with the upgraded Giant Metrewave Radio Telescope (uGMRT) which demonstrates that in-field phasing does lead to a significant improvement in sensitivity. We also show, using observations of the millisecond pulsar J1120$-$3618 that this in turn leads to a significant improvement of measurements of the Dispersion Measure and Time of Arrival. Finally, we present test observations of the GMRT discovered eclipsing black widow pulsar J1544+4937 showing that in-field phasing leads to improvement in the measurement of the cut-off frequency of the eclipse.

Phaser

10.48550/arxiv.2407.06741

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Atomic Hydrogen in Distant Galaxies

Resonance (2021)

Nissim Kanekar Aditya Chowdhury Jayaram N. Chengalur

Peculiar galaxy

10.1007/s12045-021-1192-2

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Citations (1)

Resolving the mystery of the dwarf galaxy HIZSS003

Monthly Notices of the Royal Astronomical Society Letters (2005)

Ayesha Begum Jayaram N. Chengalur И. Д. Караченцев М. Е. Шарина

The nearby galaxy HIZSS003 was recently discovered during a blind HI survey of the zone of avoidance (Henning et al. 2000). Follow up VLA as well as optical and near-IR imaging and spectroscopy (Massey et al. 2003; Silva et al. 2005) confirm that it is a low metallicity dwarf irregular galaxy. However there were two puzzling aspects of the observations, (i) current star formation, as traced by H$α$ emission, is confined to a small region at the edge of the VLA HI image and (ii) the metallicity of the older RGB stars is higher than that of the gas in HII region. We present high spatial and velocity resolution Giant Meterwave Radio Telescope (GMRT) observations that resolve these puzzles by showing that HIZSS003 is actually a galaxy pair and that the HII region lies at the center of a much smaller companion galaxy (HIZSS003B) to the main galaxy (HIZSS003A). The HI emission from these two galaxies overlaps in projection, but can be separated in velocity space. HIZSS003B has an HI mass of 2.6 X 10^6 M$_\odot$, and a highly disturbed velocity field. Since the velocity field is disturbed, an accurate rotation curve cannot be derived, however, the indicative dynamical mass is ~5 X 10^7 M$_\odot$. For the bigger galaxy HIZSS003A we derive an HI mass of 1.4 X 10^7 M$_\odot$. The velocity field of this galaxy is quite regular and from its rotation curve we derive a total dynamical mass of ~6.5 X 10^8 M$_\odot$.

Irregular galaxy

Satellite galaxy

Barred spiral galaxy

10.1111/j.1745-3933.2005.00040.x

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Citations (15)

A search for H I 21 cm absorption toward the highest redshift (z similar to 5.2) radio-loud objects

The Astronomical Journal (2007)

C. L. Carilli Ran Wang MB van Hoven K. S. Dwarakanath Jayaram N. Chengalur

Red shift

Source

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Andromeda IV, a solitary gas‐rich dwarf galaxy

Astronomische Nachrichten (2016)

И. Д. Караченцев Jayaram N. Chengalur R. Brent Tully Л. Н. Макарова М. Е. Шарина

Abstract Observations are presented of the isolated dwarf irregular galaxy And IV made with the Hubble Space Telescope Advanced Camera for Surveys and the Giant Metrewave Radio Telescope in the 21 cm H I line. We determine the galaxy distance of 7.17 ± 0.31 Mpc using the Tip of Red Giant Branch method. The galaxy has a total blue absolute magnitude of –12.81 mag, linear Holmberg diameter of 1.88 kpc, and an H I ‐disk extending to 8.4 times the optical Holmberg radius. The H I massto‐blue luminosity ratio for And IV amounts 12.9 M ⊙ /L ⊙ . From the GMRT data we derive the rotation curve for the H I and fit it with different mass models. We find that the data are significantly better fit with an iso‐thermal dark matter halo, than by an NFW halo. We also find that MOND rotation curve provides a very poor fit to the data. The fact that the isothermal dark matter halo provides the best fit to the data supports models in which star formation feedback results in the formation of a dark matter core in dwarf galaxies. The total mass‐to‐blue luminosity ratio of 162 M ⊙ /L ⊙ makes And IV among the darkest dIrr galaxies known. However, its baryonic‐to‐dark mass ratio ( M gas + M *)/ M T = 0.11 is close to the average cosmic baryon fraction of 0.15. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Red-giant branch

Dark galaxy

10.1002/asna.201512354

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Thick gas discs in faint dwarf galaxies

Monthly Notices of the Royal Astronomical Society Letters (2010)

Sambit Roychowdhury Jayaram N. Chengalur Ayesha Begum И. Д. Караченцев

We determine the intrinsic axial ratio distribution of the 'gas' disks of extremely faint M_B > -14.5 dwarf irregular galaxies. We start with the measured (beam corrected) distribution of apparent axial ratios in the HI 21cm images of dwarf irregular galaxies observed as part of the Faint Irregular Galaxy GMRT Survey (FIGGS). Assuming that the disks can be approximated as oblate spheroids, the intrinsic axial ratio distribution can be obtained from the observed apparent axial ratio distribution. We use a couple of methods to do this, and our final results are based on using Lucy's deconvolution algorithm. This method is constrained to produce physically plausible distributions, and also has the added advantage of allowing for observational errors to be accounted for. While one might a priori expect that gas disks would be thin (because collisions between gas clouds would cause them to quickly settle down to a thin disk), we find that the HI disks of faint dwarf irregulars are quite thick, with mean axial ratio ~ 0.6. While this is substantially larger than the typical value of ~ 0.2 for the 'stellar' disks of large spiral galaxies, it is consistent with the much larger ratio of velocity dispersion to rotational velocity (sigma/v_c) in dwarf galaxy HI disks as compared to that in spiral galaxies. Our findings have implications for studies of the mass distribution in and the Tully - Fisher relation for faint dwarf irregular galaxies, where it is often assumed that the gas is in a thin disk.

Dwarf spheroidal galaxy

Irregular galaxy

Velocity dispersion

10.1111/j.1745-3933.2010.00835.x

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Citations (360)

Atomic hydrogen scaling relations at $z \approx 0.35$

arXiv (Cornell University) (2023)

Apurba Bera Nissim Kanekar Jayaram N. Chengalur J. S. Bagla

The atomic hydrogen (HI) properties of star-forming galaxies in the local Universe are known to correlate with other galaxy properties via the ``HI scaling relations''. The redshift evolution of these relations serves as an important constraint on models of galaxy evolution. However, until recently, there were no estimates of the HI scaling relations at cosmological distances. Using data from a deep Giant Metrewave Radio Telescope HI 21 cm survey of the Extended Groth Strip, and the technique of spectral line stacking, we determine the scaling relation between the HI mass and the stellar mass for star-forming galaxies at $z\approx0.35$. We use this measurement, along with the main-sequence relation in galaxies, to infer the dependence of the HI depletion timescale of these galaxies on their stellar mass. We find that massive star-forming galaxies at $z\approx0.35$, with stellar mass $\rm M_* \gtrsim10^{9.5}\:M_{\odot}$, are HI-poor compared to local star-forming galaxies of a similar stellar mass. However, their characteristic HI depletion time is lower by a factor of $\approx 5$ than that of their local analogues, indicating a higher star-formation efficiency at intermediate redshifts (similar to that at $z \approx 1$). While our results are based on a relatively small cosmic volume and could thus be affected by cosmic variance, the short characteristic HI depletion timescales ($\lesssim 3$ Gyr) of massive star-forming galaxies at $z \approx 0.35$ indicate that they must have acquired a significant amount of neutral gas through accretion from the circumgalactic medium over the past four Gyr, to avoid quenching of their star-formation activity.

Stellar mass

Cosmic variance

10.48550/arxiv.2305.01389

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The Hi Mass Function of Star-forming Galaxies at z ≈ 1

The Astrophysical Journal Letters (2024)

Aditya Chowdhury Nissim Kanekar Jayaram N. Chengalur

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.

Star (game theory)

Initial mass function

10.3847/2041-8213/ad3dfe

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Citations (2)

Erratum: Thick gas discs in faint dwarf galaxies

Monthly Notices of the Royal Astronomical Society Letters (2010)

Sambit Roychowdhury Jayaram N. Chengalur Ayesha Begum И. Д. Караченцев

The Letter ‘Thick gas discs in faint dwarf galaxies’ was published in Mon. Not. R. Astron. Soc. 404, L60–L63 (2010). Unfortunately a couple of typographical errors were detected in the paper, which we correct here. The first line of the abstract should read: ‘We determine the intrinsic axial ratio distribution of the gas discs of extremely faint MB > −14.5 dwarf irregular galaxies.’ In Section 1, paragraph 2, the line referring to Ryden (2006) should read: ‘For example, Ryden (2006) showed that older popu-

Paragraph

Astron

Line (geometry)

10.1111/j.1745-3933.2010.00889.x

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The H i angular momentum–mass relation

Monthly Notices of the Royal Astronomical Society (2021)

Sushma Kurapati Jayaram N. Chengalur Marc Verheijen

We study the relationship between the H{\sc i} specific angular momentum (j$_{\rm g}$) and the H{\sc i} mass (M$_{\rm g}$) for a sample of galaxies with well measured H{\sc i} rotation curves. We find that the relation is well described by an unbroken power law \jg $\propto$ \mg$^α$ over the entire mass range (10$^{7}$-10$^{10.5}$ M$_{\odot}$), with $α= 0.89 \pm 0.05$ (scatter 0.18 dex). This is in reasonable agreement with models which assume that evolutionary processes maintain H{\sc i} disks in a marginally stable state. The slope we observe is also significantly different from both the $j \propto M^{2/3}$ relation expected for dark matter haloes from tidal torquing models and the observed slope of the specific angular momentum-mass relation for the stellar component of disk galaxies. Our sample includes two H{\sc i}-bearing ultra diffuse galaxies, and we find that their angular momentum follows the same relation as other galaxies. The only discrepant galaxies in our sample are early-type galaxies with large rotating H{\sc i} disks which are found to have significantly higher angular momentum than expected from the power law relation. The H{\sc i} disks of all these early-type galaxies are misaligned or counter-rotating with respect to the stellar disks, consistent with the gas being recently accreted. We speculate that late stage wet mergers, as well as cold flows play a dominant role in determining the kinematics of the baryonic component of galaxies as suggested by recent numerical simulations.

Stellar mass

10.1093/mnras/stab2230

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Citations (10)