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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

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

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

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 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

We study the relationship between the gas column density (Σgas) and the star formation rate (SFR) surface density (ΣSFR) for a sample of 23 extremely faint dwarf irregular galaxies drawn from the Faint Irregular Galaxy GMRT (Giant Metrewave Radio Telescope) Survey (FIGGS). Our sample galaxies have a median H i mass of 2.8 × 107 M⊙ and a median blue magnitude MB∼−13.2. ΣSFR is...

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...

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...

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

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...

Implications of 21-cm observations for damped Ly α systems

We present Giant Metrewave Radio Telescope H i 21-cm absorption observations, of candidate and confirmed damped Lyα systems. The derived spin temperatures Tspin are high, in all cases, ∼1000 K or higher. We have also collated from the published literature a list of damped absorbers for which 21-cm observations exist, and discuss the implications of the observations for the nature...

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...

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...

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...

Giant Metrewave Radio Telescope observations of low-z damped Lyα absorbers

Jayaram N. Chengalur 0 Nissim Kanekar 0 0 National Center for Radio Astrophysics (TIFR), University of Pune Campus , PO Bag 3, Ganeshkhind, Pune 411007 , India A B S T R A C T We present Giant