Results for "Jayaram N. Chengalur"

total 70724took 0.13s
Probing interstellar turbulence in spiral galaxies using HI power spectrum analysisAug 27 2012We estimate the \HI intensity fluctuation power spectrum for a sample of 18 spiral galaxies chosen from THINGS. Our analysis spans a large range of length-scales from $\sim 300 {\rm pc}$ to $\sim 16 {\rm kpc}$ across the entire galaxy sample. We find ... More
Turbulence in the Harassed Galaxy NGC 4254Apr 09 2010Galaxy harassment is an important mechanism for the morphological evolution of galaxies in clusters. The spiral galaxy NGC 4254 in the Virgo cluster is believed to be a harassed galaxy. We have analyzed the power spectrum of HI emission fluctuations from ... More
A Study of ISM of Dwarf Galaxies Using HI Power Spectrum AnalysisMay 12 2009We estimate the power spectrum of HI intensity fluctuations for a sample of 8 galaxies (7 dwarf and one spiral). The power spectrum can be fitted to a power law P_HI(U) = A U^\alpha for 6 of these galaxies, indicating turbulence is operational. The estimated ... More
Mass modelling of a superthin galaxy, FGC1540Jul 09 2018We present high resolution H{\sc i} 21cm Giant Meterwave Radio Telescope (GMRT) observations of the superthin galaxy FGC1540 with a spatial resolution of 10$''$ $\times$ 8$''$ and a spectral resolution of 1.73 kms$^{-1}$ and an rms noise of 0.9 mJy per ... More
On modelling the Fast Radio Burst (FRB) population and event rate predictionsJan 20 2016Assuming that Fast Radio Bursts (FRBs) are of extragalactic origin, we have developed a formalism to predict the FRB detection rate and the redshift distribution of the detected events for a telescope with given parameters. We have adopted FRB 110220, ... More
The HI content of star-forming galaxies at z = 0.24Jan 24 2007We use observations from the Giant Metrewave Radio Telescope (GMRT) to measure the atomic hydrogen gas content of star-forming galaxies at z = 0.24 (i.e. a look-backtime of ~3 Gyr). The sample of galaxies studied were selected from Halpha-emitting field ... More
The strange case of a sub-DLA with very little HINov 29 2004We report a deep search for HI 21cm emission from the $z= 0.00632$ sub-DLA toward PG1216+069 with the Giant Metrewave Radio Telescope. No emission was detected and our $5\sigma$ upper limit on the mass of any associated galaxy is $M_{\rm HI} \lesssim ... More
HI 21cm absorption in low z damped lyman-alpha systemsJan 23 2001We report Giant Metrewave Radio Telescope (GMRT) 21cm observations of two confirmed and one candidate low redshift damped Lyman-alpha systems (DLAS). HI absorption was detected in the two confirmed systems, at z=0.2378 and z=0.5247, with spin temperatures ... More
A search for HI in some peculiar faint dwarf galaxiesJun 27 2005We present a deep Giant Metrewave Radio Telescope (GMRT) search for HI 21 cm emission from three dwarf galaxies, viz. POX 186, SC 24 and KKR 25. Based, in part, on previous single dish HI observations, these galaxies have been classified as a BCD, a dwarf ... More
The use of OH "main" lines to constrain the variation of fundamental constantsOct 27 2003May 05 2004We describe a new technique to measure variations in the fundamental parameters $\alpha$ and $y \equiv m_e/m_p$, using the sum of the frequencies of cm-wave OH ``main'' lines. The technique is $\sim$ three orders of magnitude more sensitive than that ... More
Kinematics of two dwarf galaxies in the NGC 6946 groupJun 08 2004We present high velocity resolution (~ 1.6 km/s) Giant Meterwave Radio Telescope (GMRT) HI 21 cm synthesis images of the dwarf galaxies KK98 250 and KK98 251, as well as optical broad band images of KK98 250. We find that, despite being faint (M_B <-14), ... More
The GMRT study of extremely faint dwarf irregular galaxiesNov 24 2004We present results of deep, high velocity resolution ($\sim$1.6 kms$^{-1}$) Giant Meterwave Radio Telescope (GMRT) HI 21 cm-line observations of a sample of extremely faint (M$_B>-$12.5) dwarf irregular galaxies. Unlike previous studies, we find large ... More
Molecular gas at intermediate redshiftsNov 29 2001We present Giant Metrewave Radio Telescope (GMRT) observations of OH absorption in B3~1504+377 ($z \sim 0.673$) and PKS 1413+135 ($z \sim 0.247$). OH has now been detected in absorption towards four intermediate redshift systems, viz. the lensing galaxies ... More
Implications of 21cm observations for damped Ly-$α$ systemsNov 29 2000We present Giant Metrewave Radio Telescope HI 21cm absorption observations, of candidate and confirmed damped Lyman-$\alpha$ systems (DLAS). The derived spin temperatures (T_s) are in all cases $\sim 1000$ K or higher. We have also collated from the literature ... More
Kinematics of the dwarf irregular galaxy GR8Oct 08 2003We present deep, high velocity resolution (~1.6 km/s) Giant Meterwave Radio Telescope HI 21cm synthesis images for the faint (M_B ~ -12.1) dwarf irregular galaxy GR8. We find that the velocity field of the galaxy shows a clear systematic large scale pattern, ... More
Outflowing atomic and molecular gas at $z \sim 0.67$ towards 1504+377Oct 17 2007We report the detection of OH 1667 MHz and wide HI 21cm absorption at $z \sim 0.67$ towards the red quasar 1504+377, with the Green Bank Telescope and the Giant Metrewave Radio Telescope. The HI 21cm absorption extends over a velocity range of $\sim 600$ ... More
Constraining the variation of fundamental constants using 18cm OH linesOct 27 2003We describe a new technique to estimate variations in the fundamental constants using 18cm OH absorption lines. This has the advantage that all lines arise in the same species, allowing a clean comparison between the measured redshifts. In conjunction ... More
HI 21cm imaging of a nearby Damped Lyman-alpha systemApr 05 2002We present Giant Metrewave Radio Telescope (GMRT) HI 21cm emission images of the z=0.009 damped Lyman-alpha (DLA) absorber towards the QSO HS 1543+5921. The DLA has been earlier identified as a low surface brightness galaxy SBS 1543+593 at an impact parameter ... More
The radio - far infrared correlation in the faintest star forming dwarf galaxiesApr 15 2012We study the radio - far-infrared (FIR) correlation in a sample of faint dwarf irregular galaxies using NVSS data for 1.4 GHz radio flux, Spitzer MIPS 70 um data for FIR flux, and GALEX FUV data to estimate the star formation rates (SFR). Since our target ... More
Kinematics of Extremely Faint Dwarf GalaxiesOct 07 2003We present the results of deep, high velocity resolution (~1.6 km/s) Giant Meterwave Radio Telescope (GMRT) HI 21cm observations of extremely faint (M_B > -12.5) dwarf irregular galaxies. We find that all of our sample galaxies show systematic large scale ... More
A deep search for 21cm absorption in high redshift damped Lyman-$α$ systemsNov 28 2002We present deep GMRT 21cm absorption spectra of 10 damped Lyman-$\alpha$ systems (DLAs), of which 8 are at redshifts $z \ga 1.3$. HI absorption was detected in only one DLA, the $z = 0.5318$ absorber toward PKS 1629+12, which has been identified with ... More
ORT observations of the damped Lyman alpha system towards PKS 0201+113Nov 20 1997We report a deep radio search with the Ooty Radio Telescope (ORT) for the redshifted 21 cm absorption line from the damped Lyman alpha system seen at redshift 3.388 against the quasar PKS 0201+113. This is currently the most distant system for which a ... More
Kinematics of the faintest gas rich galaxy in the Local Group: DDO210Oct 06 2003We present deep, high velocity resolution (~1.6 km/s) Giant Meterwave Radio Telescope (GMRT) HI 21cm synthesis images of the faint (M_B ~ -10.6) local group dwarf galaxy DDO210. We find that the HI distribution in the galaxy is not axi-symmetric, but ... More
GMRT Observations of Low z Damped Lyman-alpha AbsorbersNov 04 1998We present Giant Metrewave Radio Telescope (GMRT) observations of redshifted HI 21cm absorption in two low redshift (z=0.2212, z=0.0912) damped Lyman-alpha systems seen towards the gigahertz peaked source OI 363 (z_em = 0.630). The object at z=0.0912 ... More
When are extremely metal-deficient galaxies extremely metal-deficient?Mar 31 2010Extremely metal-deficient (XMD) galaxies, by definition, have oxygen abundances \le 1/10 solar, and form a very small fraction of the local gas-rich, star-forming dwarf galaxy population. We examine their positions in the luminousity-metallicity (L-Z) ... More
Widespread acetaldehyde near the Galactic CentreApr 23 2003We present Giant Meterwave Radio Telescope images of the 1065 MHz emission from the 1_11 -> 1_10 rotational transition of acetaldehyde (CH3CHO) in the molecular cloud complex Sgr B2. Our observations are unique in that they have a high spatial resolution ... More
Variable 21cm absorption at z=0.3127Feb 24 2001We report multi-epoch GMRT HI 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 ... More
Angular Momentum Content in Gas Rich Dwarf GalaxiesFeb 09 2017We derive the specific baryonic angular momentum of five gas rich dwarf galaxies from HI kinematics complemented by stellar mass profiles. Since the gas mass of these galaxies is much larger than the stellar mass, the angular momentum can be determined ... More
A High Resolution Study of Carbon Radio Recombination Lines towards Cassiopeia AMar 13 2019Carbon Radio Recombination Lines trace the interface between molecular and atomic gas. We present GMRT observations of Carbon Radio Recombination Lines (CRRL), C$\alpha$244-C$\alpha$250 towards Cassiopeia A. We use a novel technique of stacking the emission ... More
A search for the 55 MHz OH lineApr 26 2010Jul 02 2010The OH molecule, found abundantly in the Milky Way, has four transitions at the ground state rotational level(J = 3/2) at cm wavelengths. These are E1 transitions between the F+ and F- hyperfine levels of the Lambda doublet of the J=3/2 state. There are ... More
A multiwavelength investigation of the temperature of the cold neutral mediumNov 10 2005Nov 18 2005We present measurements of the H I spin temperatures (T_s) of the Cold Neutral Medium (CNM) towards radio sources that are closely aligned with stars for which published H_2 ortho-para temperatures (T_{01}) are available from UV observations. Our sample ... More
Detection of a multi-phase ISM at $z=0.2212$Apr 19 2001Apr 20 2001We present sensitive Giant Metrewave Radio Telescope (GMRT) and high-resolution Arecibo HI 21-cm observations of the damped Lyman-$\alpha$ absorber (DLA) at $z=0.2212$ towards OI 363. The spectra are in excellent agreement and yield a spin temperature ... More
Accurate measurement of the HI column density from HI 21cm absorption-emission spectroscopyMay 04 2013We present a detailed study of an estimator of the HI column density, based on a combination of HI 21cm absorption and HI 21cm emission spectroscopy. This "isothermal" estimate is given by $N_{\rm HI,ISO} = 1.823 \times 10^{18} \int \left[ \tau_{\rm tot} ... More
Turbulence measurements from HI absorption spectraMar 17 2008May 13 2008We use the millennium Arecibo 21 cm absorption-line survey measurements to examine the issue of the non-thermal contribution to the observed Galactic HI line widths. If we assume a simple, constant pressure model for the HI in the Galaxy, we find that ... More
Extended Schmidt law holds for faint dwarf irregular galaxiesAug 07 2017The extended Schmidt law (ESL) is a variant of the Schmidt law which relates the surface densities of gas and star formation, with the surface density of stellar mass added as an extra parameter. We empirically investigate for the first time whether low ... More
Discovery of an extremely gas-rich dwarf triplet near the center of the Lynx-Cancer voidOct 03 2012Giant Metrewave Radio Telescope (GMRT) HI observations, done as part of an ongoing study of dwarf galaxies in the Lynx-Cancer void, resulted in the discovery of a triplet of extremely gas rich galaxies located near the centre of the void.The triplet members ... More
HI studies of eXtremely Metal Deficient galaxies - II: GMRT observations of SBS 1129+576Sep 06 2006We present GMRT HI observations of an eXtremely Metal Deficient (XMD) galaxy SBS 1129+576 (12 + log(O/H) = 7.41). Our HI observations show that the galaxy is strongly interacting with a companion galaxy, SBS 1129+577. A third, smaller galaxy, SDSS J113227.68+572142.3, ... More
HI and star formation in the most metal-deficient galaxiesSep 10 2008We 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 ... More
Power spectrum of HI intensity fluctuations in DDO 210Jul 17 2006We measure the power spectrum of HI intensity fluctuations in the extremely faint (M_B ~ -10.9) dwarf galaxy DDO 210 using a visibility based estimator that is well suited in very low signal to noise ratio regimes. DDO 210's HI power spectrum is well ... More
Probing fundamental constant evolution with redshifted conjugate-satellite OH linesApr 29 2010We report Westerbork Synthesis Radio Telescope and Arecibo Telescope observations of the redshifted satellite OH-18cm lines at $z \sim 0.247$ towards PKS1413+135. The "conjugate" nature of these lines, with one line in emission and the other in absorption, ... More
Stringent constraints on fundamental constant evolution using conjugate 18 cm satellite OH linesJan 23 2018We have used the Arecibo Telescope to carry out one of the deepest-ever integrations in radio astronomy, targetting the redshifted conjugate satellite OH 18 cm lines at $z \approx 0.247$ towards PKS1413+135. The satellite OH 1720 and 1612 MHz lines are ... More
The little galaxy that could: Kinematics of Camelopardalis BJan 12 2003We present deep, high velocity resolution (1.6 km/s) GMRT HI as well as optical data for the faint (M_B ~ -10.9) galaxy Camelopardalis B. We find that the HI in the galaxy has a regular velocity field, consistent with rotational motion. The implied kinematical ... More
HI in Abell 3128Apr 20 2001We discuss Australia Telescope Compact Array (ATCA) HI 21cm data for the galaxy cluster A3128. Our observations are intentionally relatively shallow, and a blind search through our data cube yields (tentative) detections of only two galaxies, of which ... More
The temperature of the diffuse HI in the Milky Way II: Gaussian decomposition of the HI 21 cm absorption spectraSep 16 2013We discuss physical conditions in Galactic neutral hydrogen based on deep, high velocity resolution interferometric HI 21 cm absorption spectroscopy towards 33 compact extra-galactic radio sources. The HI 21 cm optical depth spectra have root-mean-square ... More
Conjugate 18cm OH Satellite Lines at a Cosmological DistanceJun 04 2004Aug 02 2004We have detected the two 18cm OH satellite lines from the $z \sim 0.247$ source PKS1413+135, the 1720 MHz line in emission and the 1612 MHz line in absorption. The 1720 MHz luminosity is $L_{\rm OH} \sim 354 L_\odot$, more than an order of magnitude larger ... More
HI in very metal-poor galaxies: the SBS 0335-052 systemApr 30 2009We present Giant Metrewave Radio Telescope (GMRT), HI 21cm 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 ... More
A dwarf galaxy with a giant HI diskFeb 16 2005We present Giant Meterwave Radio Telescope (GMRT) HI 21cm images of a nearby dwarf irregular galaxy NGC 3741 (M_B ~ -13.13 mag) which show it to have a gas disk that extends to ~ 8.3 times its Holmberg radius. This makes it probably the most extended ... More
DI in the outer GalaxyJan 13 1997We report on a deep search with the Westerbork Synthesis Radio Telescope towards the galactic anticenter for the 327 MHz hyperfine transition of DI. This is a favorable direction for a search because: (i) the HI optical depth is high due to velocity crowding; ... More
GMRT observation towards detecting the Post-reionization 21-cm signalOct 21 2010We have analyzed 610 MHz GMRT observations towards detecting the redshifted 21-cm signal from z=1.32. The multi-frequency angular power spectrum C_l(Delta nu) is used to characterize the statistical properties of the background radiation across angular ... More
HI power spectrum of the spiral galaxy NGC628Nov 08 2007We have measured the HI power spectrum of the nearly face-on spiral galaxy NGC628 (M74) using a visibility based estimator. The power spectrum is well fitted by a power law $P(U)=AU^{\alpha}$, with $\alpha =- 1.6\pm0.2$ over the length scale $800 {\rm ... More
Probing Turbulence in the Interstellar Medium of GalaxiesMay 21 2009The power spectrum of HI intensity fluctuation of the interstellar medium carries information of the turbulence dynamics therein. We present a method to estimate the power spectrum of HI intensity fluctuation using radio interferometric observations. ... More
The temperature of the diffuse HI in the Milky Way I: High resolution HI 21 cm absorption studiesSep 16 2013We have carried out deep, high velocity resolution, interferometric Galactic HI 21 cm absorption spectroscopy towards 32 compact extra-galactic radio sources with the Giant Metrewave Radio Telescope (GMRT) and the Westerbork Synthesis Radio Telescope ... More
Magnetohydrodynamic turbulence in supernova remnantsNov 10 2008Jul 23 2009We present estimates of the angular power spectra of the synchrotron radiation intensity fluctuations at 6 and 20 cm for the shell type supernova remnant Cas A and the filled-centre Crab supernova remnant. We find that the intensity fluctuations of both ... More
The temperature of the WNM in the Milky WayOct 27 2003Dec 12 2003We report high spectral resolution Australia Telescope Compact Array HI 21 cm observations resulting in the detection of the warm neutral medium (WNM) of the Galaxy in absorption against two extragalactic radio sources, PKS 1814-637 and PKS 0407-658. ... More
ATCA search for 21 cm emission from a candidate damped Ly-$α$ absorber at z = 0.101Dec 04 2000We report a deep search for 21 cm emission/absorption from the $z \sim 0.101$ candidate damped Lyman-$\alpha$ system towards PKS 0439-433, using the Australia Telescope Compact Array (ATCA). The spectrum shows a weak absorption feature --- at the $3.3 ... More
Improved foreground removal in GMRT 610 MHz observations towards redshifted 21-cm tomographyAug 18 2011Foreground removal is a challenge for 21-cm tomography of the high redshift Universe. We use archival GMRT data (obtained for completely different astronomical goals) to estimate the foregrounds at a redshift ~ 1. The statistic we use is the cross power ... More
Modeling HI distribution and kinematics in the edge-on dwarf irregular galaxy KK250Nov 16 2014We model the observed vertical distribution of the neutral hydrogen (HI) in the faint (M_B ~ -13.7 mag) edge-on dwarf irregular galaxy KK250. Our model assumes that the galaxy consists of axi-symmetric, co-planar gas and stellar discs in the external ... More
Post-correlation beamformer for time-domain studies of pulsars and transientsAug 03 2018We present a detailed analysis of post-correlation beamforming (i.e. beamforming which involves only phased sums of the correlation of the voltages of different antennas in an array), and compare it with the traditionally used incoherent and phased beamforming ... More
HI 21 cm opacity fluctuations power spectra towards Cassiopeia AFeb 22 2010Jun 22 2010The angular power spectrum of HI 21 cm opacity fluctuations is a useful statistic for quantifying the observed opacity fluctuations as well as for comparing these with theoretical models. We present here the HI 21 cm opacity fluctuation power spectrum ... More
A metallicity-spin temperature relation in damped Lyman-$α$ systemsSep 14 2009We report evidence for an anti-correlation between spin temperature $T_s$ and metallicity [Z/H], detected at $3.6 \sigma$ significance in a sample of 26 damped Lyman-$\alpha$ absorbers (DLAs) at redshifts $0.09 < z < 3.45$. The anti-correlation is detected ... More
Thick gas discs in faint dwarf galaxiesFeb 24 2010Apr 26 2010We 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 ... More
Angular momentum of dwarf galaxiesMay 24 2018Mass and specific angular momentum are two fundamental physical parameters of galaxies. We present measurements of the baryonic mass and specific angular momentum of 11 void dwarf galaxies derived from neutral hydrogen (H{\sc i}) synthesis data. Rotation ... More
GMRT Observations of Interstellar Clouds in the 21cm line of Atomic HydrogenMar 17 2001Nearby interstellar clouds with high (|v| >/= 10 km/s) random velocities although easily detected in NaI and CaII lines have hitherto not been detected (in emission or absorption) in the HI 21cm line. We describe here deep Giant Metrewave Radio Telescope ... More
FLAGCAL:A flagging and calibration package for radio interferometric dataNov 28 2011We describe a flagging and calibration pipeline intended for making quick look images from GMRT data. The package identifies and flags corrupted visibilities, computes calibration solutions and interpolates these onto the target source. These flagged ... More
Star formation in extremely faint dwarf galaxiesApr 17 2009We study the relationship between the gas column density (derived from GMRT 21 cm data) and the star formation rate surface density (derived from publicly available GALEX data) for a sample of 23 extremely faint dwarf irregular galaxies drawn from the ... More
The HI column density distribution function in faint dwarf galaxiesNov 27 2012We present the HI column density distribution function,\fnh, as measured from dwarf galaxies observed as part of the Faint Irregular Galaxy GMRT (FIGGS) survey. We find that the shape of the dwarf galaxy \fnh\ is significantly different from the \fnh\ ... More
HI and OH absorption at z=0.89Apr 05 1999Apr 06 1999We report on WSRT observations of HI and OH absorption at z=0.885 towards the radio lens PKS 1830-21, mm wave transitions of several molecular species have already been observed at this redshift. At mm wavelengths the source structure is dominated by ... More
UGC 3672: An unusual merging triplet of gas-rich galaxies in the Lynx-Cancer voidNov 04 2016We present HI 21cm and optical observations of UGC 3672 which is located near the centre of the nearby Lynx-Cancer void. We find that UGC 3672 consists of an approximately linearly aligned triplet of gas rich dwarfs with large scale velocity continuity ... More
A new 21-cm absorber identified with an $L \sim L^\star$ galaxyDec 13 2001We present Giant Metrewave Radio Telescope (GMRT) observations of redshifted 21-cm absorption from the $z=0.437$ metal line absorption system towards PKS 1243-072. HI absorption is clearly detected; the absorption profile has a velocity spread of $\sim ... More
Foregrounds for redshifted 21 cm studies of reionization: GMRT 153 MHz observationsJan 16 2008Foreground subtraction is the biggest challenge for future redshifted 21 cm observations to probe reionization. We use a short GMRT observation at 153 MHz to characterize the statistical properties of the background radiation across ~ one degree to sub-arcminutes ... More
The Scale Height of NGC 1058 Measured from its HI Power SpectrumMay 10 2009We have measured the HI power spectrum of the nearly face-on spiral galaxy NGC 1058 from radio-interferometric observations using a visibility based estimator. The power spectrum is well fitted by two different power laws $P(U)=AU^{\alpha}$, one with ... More
HI 21cm-line observations with the GMRT towards interstellar clouds previously seen in optical absorptionApr 11 2000We have made HI 21cm-line absorption measurements using the GMRT towards 15 directions in the Galaxy which are known to have high random velocity clouds as seen in the optical absorption lines of CaII and NaI. For the first time, in 6 out of these 15 ... More
A slow bar in the dwarf irregular galaxy NGC 3741Aug 14 2013Using the Tremaine-Weinberg method, we measure the speed of the HI bar seen in the disk of NGC 3741. NGC 3741 is an extremely gas rich galaxy with an {H\,{\sc i}} disk which extends to about 8.3 times its Holmberg radius. It is also highly dark matter-dominated. ... More
Polarimetric imaging with the GMRTOct 28 2010We present the first set of polarimetric images made with the GMRT. These were obtained as part of the program to commission the polarization mode at the telescope. We find that the instrumental polarization leakage at the GMRT varies with frequency. ... More
FRB event rate predictions for the Ooty Wide Field ArrayMar 02 2017We developed a generic formalism to estimate the event rate and the redshift distribution of Fast Radio Bursts (FRBs) in our previous publication (Bera et al. 2016), considering FRBs are of an extragalactic origin. In this paper we present (a) the predicted ... More
Non-linear Redundancy CalibrationOct 05 2013For radio interferometric arrays with a sufficient number of redundant spacings the multiplicity of measurements of the same sky visibility can be used to determine both the antenna gains as well as the true visibilities. Many of the earlier approaches ... More
Small Bites: Star formation recipes in extreme dwarfsMar 31 2011We study the relationship between the gas column density (Sigma_HI) and the star formation rate surface density (Sigma_SFR) for a sample of extremely small (M_B ~ -13, Delta V_50 ~ 30 km/s) dwarf irregular galaxies. We find a clear stochasticity in the ... More
Baryonic Tully-Fisher Relation for Extremely Low Mass GalaxiesJan 23 2008We study Tully-Fisher relations for a sample that combines extremely faint (M_B > -14.0) galaxies along with bright (i.e. L_*) galaxies. Accurate (~ 10%) distances, I band photometry, and B-V colors are known for the majority of the galaxies in our sample. ... More
The intrinsic shapes of dwarf irregular galaxiesAug 28 2013We use the measured B band axial ratios of galaxies from an updated catalog of Local Volume galaxies to determine the intrinsic shape of dwarf irregular galaxies (de Vacouleurs' morphological types 8, 9 and 10). We find that the shapes change systematically ... More
Cold HI in faint dwarf galaxiesDec 20 2015We present the results of a study of the amount and distribution of cold atomic gas, as well its correlation with recent star formation in a sample of extremely faint dwarf irregular galaxies. Our sample is drawn from the Faint Irregular Galaxy GMRT Survey ... More
A radio Search for high redshift HI absorptionDec 12 1995Ground based optical observations have yielded considerable information on the statistics of damped-lyman alpha systems. In particular these systems are known to be the dominant repository of the observed neutral gas at high redshift. However, particularly ... More
GMRT observation of neutral atomic hydrogen gas in the COSMOS field at $z \sim 0.37$May 06 2016We present the results of HI spectral stacking analysis of Giant Metrewave Radio Telescope (GMRT) observations targeting the COSMOS field. The GMRT data cube contains 474 field galaxies with redshifts known from the zCOSMOS-bright 10k catalogue. Spectra ... More
Life in the last lane: Star formation and chemical evolution in an extremely gas-rich dwarfNov 10 2007We present an analysis of HI, H-alpha, and oxygen abundance data for NGC 3741. This galaxy has a very extended gas disk (~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 ... More
FIGGS: Faint Irregular Galaxies GMRT Survey - Overview, observations and first resultsFeb 27 2008The Faint Irregular Galaxies GMRT Survey (FIGGS) is a Giant Metrewave Radio Telescope (GMRT) based HI imaging survey of a systematically selected sample of extremely faint nearby dwarf irregular galaxies. The primary goal of FIGGS is to provide a comprehensive ... More
FIGGS2: An HI survey of extremely faint irregular galaxiesSep 05 2016We present the observations and first results from the FIGGS2 survey. FIGGS2 is an extension of the earlier Faint Irregular Galaxies GMRT survey (FIGGS) towards faint luminosity end. The sample consists of 20 galaxies of which 15 were detected in HI 21cm ... More
HI in XMD Galaxies III. GMRT observations of BCG HS0822+3542Aug 04 2006We present Giant Metrewave Radio Telescope (GMRT) HI 21-cm line data for the smallest known eXtremely Metal Deficient (XMD) blue compact galaxy (BCG) HS0822+3542. From HST imaging it has been suggested that HS0822+3542 actually consists of two still smaller ... More
Atomic hydrogen, star formation and feedback in the lowest mass Blue Compact Dwarf galaxiesJul 12 2012We present the results from a search for HI emission from a sample of newly discovered dwarf galaxies in the M81 group. HI is detected in three galaxies, all of which are classified as BCDs. The HI masses of these galaxies are ~ 10^6 M_sun, making these ... More
Resolving the mystery of the dwarf galaxy HIZSS003Mar 06 2005The 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 ... More
Gas rich galaxies from the FIGGS surveyNov 14 2007The FIGGS (Faint Irregular Galaxy GMRT Survey) is aimed at creating a multi-wavelength observational data base for a volume limited sample of the faintest gas rich galaxies. In this paper we discuss two very gas rich galaxies that were observed as part ... More
FIGGS: Faint Irregular Galaxies GMRT SurveyNov 12 2007The Faint Irregular Galaxies GMRT Survey (FIGGS) is a large program aimed at providing a comprehensive and statistically robust characterisation of the neutral ISM properties of faint (M_B > -14.5), nearby, gas rich, dwarf irregular galaxies using the ... More
Gas distribution, kinematics and star formation in faint dwarf galaxiesNov 09 2005We compare the gas distribution, kinematics and the current star formation in a sample of 10 very faint (-13.37 < M_B < -9.55) dwarf galaxies. For 5 of these galaxies we present fresh, high sensitivity, GMRT HI 21cm observations. For all our galaxies ... More
The relation between atomic gas and star formation rate densities in faint irregular galaxiesSep 03 2014We use data for faint (M_B > -14.5) dwarf irregular galaxies drawn from the FIGGS survey to study the correlation between the atomic gas density (Sigma_gas,atomic) and star formation rate (Sigma_SFR) in the galaxies. The estimated gas phase metallicity ... More
Characterizing Foreground for redshifted 21-cm radiation: 150 MHz GMRT observationsAug 08 2012Foreground removal is a major challenge for detecting the redshifted 21-cm neutral hydrogen (HI) signal from the Epoch of Reionization (EoR). We have used 150 MHz GMRT observations to characterize the statistical properties of the foregrounds in four ... More
The spatially resolved Kennicutt-Schmidt relation in the HI dominated regions of spiral and dwarf irregular galaxiesMar 09 2015We study the Kennicutt-Schmidt relation between average star formation rate and average cold gas surface density in the Hi dominated ISM of nearby spiral and dwarf irregular galaxies. We divide the galaxies into grid cells varying from sub-kpc to tens ... More
New Lessons from the HI Size-Mass Relation of GalaxiesMay 05 2016We revisit the HI size-mass (D$_{\rm HI}$-M$_{\rm HI}$) relation of galaxies with a sample of more than 500 nearby galaxies covering over five orders of magnitude in HI mass and more than ten $B$-band magnitudes. The relation is remarkably tight with ... More
Andromeda IV, a solitary gas-rich dwarf galaxyDec 18 2015Observations 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 HI line. We determine the galaxy distance of $7.17\pm0.31$ Mpc ... More
HI 21cm emission from the sub-damped Lyman-alpha absorber at z=0.0063 towards PG1216+069Aug 12 2015We present HI 21cm emission observations of the z ~ 0.00632 sub-damped Lyman-alpha absorber (sub-DLA) towards PG1216+069 made using the Arecibo Telescope and the Very Large Array (VLA). The Arecibo 21cm spectrum corresponds to an HI mass of ~ 3.2x10^7 ... More
Neutral atomic hydrogen (HI) gas evolution in field galaxies at z ~ 0.1 and 0.2Aug 07 2013We measure the neutral atomic hydrogen (HI) gas content of field galaxies at intermediate redshifts of z ~ 0.1 and z ~ 0.2 using hydrogen 21-cm emission lines observed with the Westerbork Synthesis Radio Telescope (WSRT). In order to make high signal-to-noise ... More
Neutral hydrogen (HI) gas content of galaxies at $z \approx 0.32$Sep 22 2017We use observations made with the Giant Metrewave Radio Telescope (GMRT) to probe the neutral hydrogen (HI) gas content of field galaxies in the VIMOS VLT Deep Survey (VVDS) 14h field at $z \approx 0.32$. Because the HI emission from individual galaxies ... More
Simulated foreground predictions for HI at z = 3.35 with the Ooty Wide Field Array: I. Instrument and the foregroundsJul 17 2017Foreground removal is the most important step in detecting the large-scale redshifted HI 21-cm signal. Modelling foreground spectra is challenging and is further complicated by the chromatic response of the telescope. We present a multi-frequency angular ... More