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Accurate measurement of the H i column density from H i 21 cm absorption-emission spectroscopy

Accurate measurement of the H I column density from H I 21 cm absorption-emission spectroscopy Jayaram N. Chengalur 1 ‹ Nissim Kanekar 1 Nirupam Roy 0 0 Max-Planck-Institut fu ̈r Radioastronomie

When are extremely metal-deficient galaxies extremely metal deficient?

B. Ekta 0 Jayaram N. Chengalur 0 0 National Centre for Radio Astrophysics , Post Bag 3, Ganeshkhind, Pune 411 007 , India A B S T R A C T Extremely metal-deficient (XMD) galaxies, by definition

A search for the 55-MHz OH line

Visweshwar Ram Marthi 0 Jayaram N. Chengalur 0 0 National Centre for Radio Astrophysics, Tata Institute of Fundamental Research , Pune 411 007 , India A B S T R A C T The OH molecule, found

H i in isolated extremely metal-deficient galaxies

B. Ekta 0 Jayaram N. Chengalur 0 0 National Centre for Radio Astrophysics , Post Bag 3, Ganeshkhind, Pune 411 007 , India A B S T R A C T We present Giant Metrewave Radio Telescope H I observations

Improved foreground removal in GMRT 610 MHz observations towards redshifted 21-cm tomography

Foreground removal is a challenge for 21-cm tomography of the high-redshift Universe. We use archival Giant Metrewave Radio Telescope (GMRT) data (obtained for completely different astronomical goals) to estimate the foregrounds at a redshift of ∼1. The statistic we use is the cross power spectrum between two frequencies separated by Δν at the angular multipole ℓ, or equivalently...

GMRT observation towards detecting the post-reionization 21-cm signal

The redshifted 21-cm signal from neutral hydrogen (H i) is an important future probe of the high-redshift Universe. We have analysed 610 MHz Giant Metrewave Radio Telescope (GMRT) observations towards detecting this signal from z= 1.32. The multi-frequency angular power spectrum Cℓ(Δν) is used to characterize the statistical properties of the background radiation across angular...

Atomic hydrogen, star formation and feedback in the lowest mass blue compact dwarf galaxies

We present the results from a search for H i emission from a sample of newly discovered dwarf galaxies in the M81 group. H i is detected in three galaxies, all of which are classified as blue compact dwarf galaxies (BCDs). The H i masses of these galaxies are ∼106 M⊙, making them some of the lowest mass BCDs known. For these three galaxies far-ultraviolet (FUV) images (from GALEX...

H i in very metal-poor galaxies: the SBS 0335–052 system

We present Giant Metrewave Radio Telescope, H i 21 cm observations of SBS 0335–052E and SBS 0335–052W, a close pair of dwarf galaxies, which are further unusual in being the most metal-poor star-forming galaxies known. We present images at several angular resolutions, ranging from ∼40 to 4 arcsec. These images show that SBS 0335–052 is a strongly interacting system, with a faint...

H i and star formation in the most metal-deficient galaxies

We present Giant Metrewave Radio Telescope (GMRT) observations for three (viz., DDO 68, SDSS J2104−0035 and UGC 772) of the six most metal-deficient actively star-forming galaxies known. Although there is a debate as to whether these galaxies are undergoing their first episode of star formation or not, they are ‘young’ in the sense that their interstellar medium is chemically...

A study of interstellar medium of dwarf galaxies using H i power spectrum analysis

We estimate the power spectrum of H i intensity fluctuations for a sample of eight galaxies (seven dwarf and one spiral). The power spectrum can be fitted to a power-law for six of these galaxies, indicating turbulence is operational. The estimated best-fitting value for the slope ranges from ∼−1.5 (AND IV, NGC 628, UGC 4459 and GR 8) to ∼−2.6 (DDO 210 and NGC 3741). We interpret...

Star formation in extremely faint dwarf galaxies

C 2009 The Authors. Journal compilation C 2009 RAS Ayesha Begum2 Sambit Roychowdhury 2 Jayaram N. Chengalur 2 Igor D. Karachentsev 0 0 Special Astrophysical Observatory, Russian Academy of Sciences

Foregrounds for redshifted 21-cm studies of reionization: Giant Meter Wave Radio Telescope 153-MHz observations

1 Jayaram N. Chengalur 0 0 National Centre for Radio Astrophysics , TIFR, Post Bag 3, Ganeshkhind, Pune 411 007 , India 1 Department of Physics and Meteorology & Centre for Theoretical Studies, IIT

A search for H i in some peculiar faint dwarf galaxies

Jayaram N. Chengalur 0 0 National Centre for Radio Astrophysics , Post Bag 3, Ganeshkhind, Pune 411 007 , India A B S T R A C T We present a deep Giant Metrewave Radio Telescope (GMRT) search for H

H i studies of extremely metal-deficient galaxies – II. Giant Metrewave Radio Telescope observations of SBS 1129+576

We present Giant Metrewave Radio Telescope H i observations of an extremely metal-deficient galaxy SBS 1129+576. SBS 1129+576 has a weighted mean oxygen abundance of 12 + log (O/H) = 7.41 ± 0.07, or 1/18 of the solar value. Our H i observations show that the galaxy is strongly interacting with a companion (projected separation ∼27 kpc) galaxy, SBS 1129+577. H i emission from a...

Baryonic Tully–Fisher relation for extremely low mass Galaxies

We study Tully–Fisher (TF) relations for a sample that combines extremely faint (MB < −14) galaxies along with bright (i.e. ∼L*) galaxies. Accurate (∼10 per cent) distances, I-band photometry and B−V colours are known for the majority of the galaxies in our sample. The faint galaxies are drawn from the Faint Irregular Galaxy GMRT survey (FIGGS), and we have H i rotation...

FIGGS: Faint Irregular Galaxies GMRT Survey – overview, observations and first results

The Faint Irregular Galaxies GMRT Survey (FIGGS) is a Giant Metrewave Radio Telescope (GMRT) based H i imaging survey of a systematically selected sample of extremely faint nearby dwarf irregular galaxies. The primary goal of FIGGS is to provide a comprehensive and statistically robust characterization of the neutral interstellar medium properties of faint, gas-rich dwarf...

Life in the last lane: star formation and chemical evolution in an extremely gas rich dwarf

We present an analysis of H i, Hα and oxygen abundance data for NGC 3741. This galaxy has a very extended gas disc (∼8.8 times the Holmberg radius), and a dark-to-luminous (i.e. stellar) mass ratio of ∼149, which makes it one of the ‘darkest’ dwarf irregular galaxies known. However, its ratio of baryon (i.e. gas + stellar) mass to dark mass is typical of that in galaxies. Our new...

H i in extremely metal deficient galaxies – III. Giant Metrewave Radio Telescope observations of blue compact galaxy HS 0822+3542

We present the results of Giant Metrewave Radio Telescope H i 21-cm line observations of the extremely metal deficient (XMD) blue compact galaxy (BCG) HS 0822+3542. HS 0822+3542 is the smallest known XMD galaxy; from Hubble Space Telescope (HST) imaging, it has been suggested that it actually consists of two still smaller (∼100 pc sized) ultra-compact dwarfs that are in the...

Variable 21-cm absorption at z=0.3127

We report multi-epoch Giant Metrewave Radio Telescope (GMRT) H I observations of the z = 0.3127 damped absorber towards the quasar PKS 1127−145, which reveal variability in both the absorption profile and the flux of the background source, over a time-scale of a few days. The observed variations cannot be explained by simple interstellar scintillation (ISS) models where there are...

The temperature of the warm neutral medium in the Milky Way

We report high-spectral-resolution Australia Telescope Compact Array (ATCA) H i 21-cm observations resulting in the detection of the warm neutral medium (WNM) of the Galaxy in absorption against two extragalactic radio sources, PKS 1814−637 and PKS 0407−658. The two lines of sight were selected on the basis of the simplicity of their absorption profiles and the strength of the...