HI Line Profiles Research Articles

Low Surface Brightness Galaxy catalogue selected from the α.40-SDSS DR7 Survey and Tully–Fisher relation

We present a catalogue of an HI-selected sample of 1129 low surface brightness galaxies (LSBGs) searched from the alpha.40-SDSS DR7 survey. This sample, consisting of various types of galaxies in terms of luminosity and morphology, has extended the parameter space covered by the existing LSBG samples. Based on a subsample of 173 LSBGs which are selected from our entire LSBG sample to have the 2-horn shapes of the HI line profiles, minor-to-major axial ratios (b/a) less than 0.6 and signal-to-noise ratio (S/N) of HI detection greater than 6.5, we investigated the Tully-Fisher relation (TFr) of LSBGs in the optical B, g and r bands and near-infrared J, H and K bands as well. In optical bands, the LSBG subsample follows the fundamental TFr which was previously defined for normal spiral galaxies. In NIR bands, the TFrs for our LSBG subsample are slightly different from the TFrs for the normal bright galaxies. This might be due to the internal extinction issue. Furthermore, the mass-to-light ratio (M/L),disk scale length (h) and mass surface density (sigma) for our LSBG subsample were deduced from the optical TFr results. Compared with High Surface Brightness Galaxies(HSBGs), our LSBGs have higher M/L, larger h and lower sigma than HSBGs.

H α and H β Raman scattering line profiles of the symbiotic star AG Pegasi

The H$\alpha$ and H$\beta$ line profiles of the symbiotic star AG Peg observed on 1998 September (phase $\phi$ = 10.24), display the top narrow double Gaussian and bottom broad (FWHM of 200 -- 400 kms$^{-1}$) components. The photo-ionization model indicated that the ionized zone, responsible for the hydrogen Balmer and Lyman lines, is radiation-bounded, with a hydrogen gas number density of $n_{\rm H} \sim 10^{9.85}$ cm$^{-3}$ and a gas temperature of T$_e$ = 12\,000 -- 15\,000~K. We carried out Monte Carlo simulations to fit the Raman scattering broad wings, assuming that the hydrogen Ly$\beta$ and Ly$\gamma$ lines emitted within the radiation-bounded HII zone around a white dwarf have the same double Gaussian line profile shape as the hydrogen Balmer lines. The simulation shows that the scattering HI zones are attached to (or located just outside of) the inner HII shells. The best fit to the observed broad HI line profiles indicates that the column density of the scattering neutral zone is $N_{\rm H} \simeq $ 3 -- 5 $\times$ 10$^{19}$ cm$^{-2}$. We examined whether the geometrical structure responsible for the observed H$\alpha$ and H$\beta$ line profiles is a bipolar conical shell structure, consisting of the radiation-bounded ionized zone and the outer material bounded neutral zone. The expanding bipolar structure might be two opposite regions of the common envelope or the outer shell of the Roche lobe around the hot white dwarf, formed through the mass inflows from the giant star and pushed out by the fast winds from the hot white dwarf.

Distribution and kinematics of atomic and molecular gas inside the solar circle

The detailed distribution and kinematics of the atomic and the CO-bright molecular hydrogen in the disc of the Milky Way inside the Solar circle are derived under the assumptions of axisymmetry and pure circular motions. We divide the Galactic disc into a series of rings, and assume that the gas in each ring is described by four parameters: its rotation velocity, velocity dispersion, midplane density and its scale height. We fit these parameters to the Galactic HI and CO (J=1-0) data by producing artificial HI and CO line-profiles and comparing them with the observations. Our approach allows us to fit all parameters to the data simultaneously without assuming a-priori a radial profile for one of the parameters. We present the distribution and kinematics of the HI and H2 in both the approaching (QIV) and the receding (QI) regions of the Galaxy. Our best-fit models reproduces remarkably well the observed HI and CO longitude-velocity diagrams up to a few degrees of distance from the midplane. With the exception of the innermost 2.5 kpc, QI and QIV show very similar kinematics. The rotation curves traced by the HI and H2 follow closely each other, flattening beyond R=6.5 kpc. Both the HI and the H2 surface densities show a) a deep depression at 0.5<R<2.5 kpc, analogous to that shown by some nearby barred galaxies, b) local overdensities that can be interpreted in terms of spiral arms or ring-like features in the disk. The HI (H2) properties are fairly constant in the region outside the depression, with typical velocity dispersion of 8.9+/-1.1 (4.4+/-1.2) km/s, density of 0.43+/-0.11 (0.42+/-0.22) cm-3 and HWHM scale height of 202+/-28 (64+/-12) pc. We also show that the HI opacity in the LAB data can be accounted for by using an `effective' spin temperature of about 150 K: assuming an optically thin regime leads to underestimate the HI mass by about 30%.

HI emission from the red giant Y CVn with the VLA and FAST

Imaging studies with the Very Large Array (VLA) have revealed HI emission associated with the extended circumstellar shells of red giants. We analyze the spectral map obtained on Y CVn, a J-type carbon star on the Asymptotic Giant Branch. The HI line profiles can be interpreted with a model of a detached shell resulting from the interaction of a stellar outflow with the local interstellar medium. We reproduce the spectral map by introducing a distortion along a direction corresponding to the star’s motion in space. We then use this fitting to simulate observations expected from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), and discuss its potential for improving our description of the outer regions of circumstellar shells.

X-shooter spectroscopy of young stellar objects

Hydrogen recombination emission lines commonly observed in accreting young stellar objects represent a powerful tracer for the gas conditions in the circumstellar structures. Here we perform a study of the HI decrements and line profiles, from the Balmer and Paschen lines detected in the X-Shooter spectra of a homogeneous sample of 36 T Tauri stars in Lupus, the accretion and stellar properties of which were already derived in a previous work. We aim to obtain information on the gas physical conditions to derive a consistent picture of the HI emission mechanisms in pre-main sequence low-mass stars. We have empirically classified the sources based on their HI line profiles and decrements. We identified four Balmer decrement types (classified as 1, 2, 3, and 4) and three Paschen decrement types (A, B, and C), characterised by different shapes. We first discussed the connection between the decrement types and the source properties and then compared the observed decrements with predictions from recently published local line excitation models. One third of the objects show lines with narrow symmetric profiles, and present similar Balmer and Paschen decrements (straight decrements, types 2 and A). Lines in these sources are consistent with optically thin emission from gas with hydrogen densities of order 10^9 cm^-3 and 5000<T<15000 K. These objects are associated with low mass accretion rates. Type 4 (L-shaped) Balmer and type B Paschen decrements are found in conjunction with very wide line profiles and are characteristic of strong accretors, with optically thick emission from high-density gas (log n_H > 11 cm^-3). Type 1 (curved) Balmer decrements are observed only in three sub-luminous sources viewed edge-on, so we speculate that these are actually reddened type 2 decrements. About 20% of the objects present type 3 Balmer decrements (bumpy), which cannot be reproduced with current models.

A study of the shell of Nova V2659 Cyg

Results of a study of the shell of Nova V2659 Cyg based on spectrophotometric observations carried out over a year and a half after its eruption are presented. The physical conditions in the nova shell have been studied. The electron temperature (9000 K) and density (5 × 106 cm−3) in the nebular stage have been estimated, together with the abundances of helium, oxygen, nitrogen, neon, argon, and iron. The abundances of nitrogen, oxygen, neon, and argon are enhanced relative to the solar values. The relative abundances are [N/H] = 2.26 ± 0.25 dex, [O/H] = 1.66 ± 0.35 dex, [Ne/H] = 0.78 ± 0.25 dex, and [Ar/H] = 0.32 ± 0.38 dex. The estimated mass of oxygen and total mass of the emitting shell are ≈1 × 10−4 M ⊙ and ≈3 × 10−4 M ⊙, respectively. In the period of chaotic brightness oscillations, the maximum velocity of the shell expansion derived from the radial velocities of the absorption components of the HI and FeII line profiles increased by ≈400 km/s 41 days after the maximum, and by ≈200 km/s 101 days after the maximum, reaching 1600 km/s in both cases.

The different baryonic Tully-Fisher relations at low masses.

We compare the Baryonic Tully-Fisher relation (BTFR) of simulations and observations of galaxies ranging from dwarfs to spirals, using various measures of rotational velocity Vrot. We explore the BTFR when measuring Vrot at the flat part of the rotation curve, Vflat, at the extent of H i gas, Vlast, and using 20percent (W20) and 50percent (W50) of the width of H i line profiles. We also compare with the maximum circular velocity of the parent halo, [Formula: see text], within dark matter only simulations. The different BTFRs increasingly diverge as galaxy mass decreases. Using Vlastone obtains a power law over four orders of magnitude in baryonic mass, with slope similar to the observed BTFR. Measuring Vflat gives similar results as Vlast when galaxies with rising rotation curves are excluded. However, higher rotation velocities would be found for low-mass galaxies if the cold gas extended far enough for Vrot to reach a maximum. W20 gives a similar slope as Vlast but with slightly lower values of Vrot for low-mass galaxies, although this may depend on the extent of the gas in your galaxy sample. W50 bends away from these other relations towards low velocities at low masses. By contrast, [Formula: see text] bends towards high velocities for low-mass galaxies, as cold gas does not extend out to the radius at which haloes reach [Formula: see text]. Our study highlights the need for careful comparisons between observations and models: one needs to be consistent about the particular method of measuring Vrot, and precise about the radius at which velocities are measured.

Velocity resolved [C ii] spectroscopy of the center and the BCLMP 302 region of M 33 (HerM 33es)

We aim to understand the contribution of the ionized, atomic and molecular phases of the ISM to the [CII] emission from clouds near the dynamical center and the BCLMP302 HII region in the north of the nearby galaxy M33 at a spatial resolution of 50pc. We combine high resolution [CII] spectra taken with the HIFI spectrometer onboard the Herschel satellite with [CII] Herschel-PACS maps and ground-based observations of CO(2-1) and HI. All data are at a common spatial resolution of 50pc. Typically, the [CII] lines have widths intermediate between the narrower CO(2-1) and broader HI line profiles. We decomposed the [CII] spectra in terms of contribution from molecular and atomic gas detected in CO(2-1) and HI, respectively. We find that the relative contribution of molecular and atomic gas traced by CO(2-1) and HI varies depends mostly on the local physical conditions and geometry. We estimate that 11-60% and 5-34% of the [CII] intensities in the center and in BCLMP302, respectively, arise at velocities showing no CO(2-1) or HI emission and could arise in CO-dark molecular gas. The deduced strong variation in the [CII] emission not associated with CO and HI cannot be explained in terms of differences in A_v, far-ultraviolet radiation field, and metallicity between the two studied regions. Hence the relative amounts of diffuse (CO-dark) and dense molecular gas possibly vary on spatial scales smaller than 50pc. Based on the emission measure observed at radio wavelengths we estimate the contribution of ionized gas at a few positions to lie between 10-25%. The correlations between the intensities of tracers corresponding to the same velocity range as [CII], differ from the correlation derived from PACS data. The results in this paper emphasize the need for velocity-resolved observations to discern the contribution of different components of the ISM to [CII] emission. (abridged)

Spectroscopic Study of the Symbiotic Star CI Cyg

Department of Earth Science Education (Astronomy), Chungbuk National University,Chungbuk 361-763, KoreaAbstract: We secured the high dispersion spectra of the symbiotic star CI Cyg. The HI, HeI, and HeII line profiles wereanalyzed using the relatively long exposure data including 1800 sec (Sep. 12, 1998, phase=0.90), 3600 sec (Aug. 12,2002, φ=0.47), and 1800 sec (Oct. 21, 2009, φ=0.54). Although a minor outburst was reported in 2008, our threeobservation periods were generally known to be quiescent in earlier photometric studies. With the help of hydrodynamicsimulations, we identified the two emission zones responsible for the blue- and red-shifted line components: (a) anaccretion disk around a hot white dwarf star which consists of the outer cool HeI emission zone and the inner hot HeIIemission part, and (b) a high density zone near the inner Lagrangian point responsible for the HeI line flux variation andthe broadening of its line profile. The HeII line fluxes indicate that the HeII emission zone of the accretion disk isrelatively stable, implying a constant gas inflow from the giant star throughout the quiescent period. The 2002 HeI datashowed that the notable mass flow activity through the inner Lagrangian point occurred during this period and its fluxintensity became strongest, whereas the HeII line width in the same period indicates that its flow activity forced theaccretion disk to expand. The [OIII] lines were observed in 1998 but not detected in 2002 and 2009, implying thedisappearance of the low density zone. Based on our kinematical studies upon the line profiles, we conclude that CI Cygwas stable in 1998 among the three observation periods selected in this research.Keywords: spectroscopy, line profile, symbiotic star, CI Cyg, SPH simulation.

DRIVERS OF H I TURBULENCE IN DWARF GALAXIES

Neutral hydrogen (HI) velocity dispersions are believed to be set by turbulence in the interstellar medium (ISM). Although turbulence is widely believed to be driven by star formation (SF), recent studies have shown that this driving mechanism may not be dominant in regions of low SF rate surface density (SFRSD), such as found in dwarf galaxies or the outer regions of spirals. We have generated average HI line profiles in a number of nearby dwarfs and low-mass spirals by co-adding HI spectra in regions with either a common radius or SFRSD. We find that the spatially-resolved superprofiles are composed of a central narrow peak (5-15 km/s) with higher velocity wings to either side. With the assumption that the central peak reflects the turbulent velocity dispersion, we compare HI kinematics to local ISM properties, including surface mass densities and measures of SF. The HI velocity dispersion is correlated most strongly with surface mass density, which points at a gravitational origin for turbulence, but it is unclear which instabilities can operate efficiently in these systems. SF energy is produced at a level sufficient to drive HI turbulent motions where SFRSD > 10^-4 Msun yr^-1 kpc^-2. At low SF intensities, SF does not supply enough energy for turbulence, nor does it uniquely determine the velocity dispersion. Nevertheless, SF appears to provide a lower threshold for HI velocity dispersions. We find that coupling efficiency decreases with increasing SFRSD, consistent with a picture where SF couples to the ISM with constant efficiency, but that less of that energy is found in HI at higher SFRSD. We examine a number of potential drivers of HI turbulence, including SF, gravitational instabilities, the magnetorotational instability, and accretion, and find that no single mechanism can drive the observed levels of turbulence at low SFRSD. We discuss possible solutions to this conundrum.

Narrow-line H i and cold structures in the interstellar medium

Context. In the HI line profiles in the Leiden-Argentina-Bonn (LAB) all-sky database, we have found a population of very cold HI clouds. So far, the role of these clouds in the interstellar medium (ISM) has remained unclear. Aims. In this paper, we attempt to confirm the existence of the narrow-line HI emission (NHIE) clouds by using the data from the Parkes Galactic all-sky survey (GASS) and try to find their place among other coldest constituents of the ISM. Methods. We repeat the search of NHIE with the GASS data and derive or compile some preliminary estimates for the distribution, temperatures, distances, linear sizes, column and number densities, masses, and the composition of NHIE clouds, and compare these data with corresponding estimates for HI self-absorption (HISA) features, the Planck cold clumps (CC), and infrared dark clouds (IRDC). Results. We demonstrate that from LAB and GASS we can separate comparable NHIE complexes, and the properties of the obtained NHIE clouds are very similar to those of HISA features, but both of these types of clouds are somewhat warmer and more extended and have lower densities than the cores in the Planck CC and IRDC. Conclusions. We conclude that NHIE may be the same type of clouds as HISA, but in different observing conditions, in the same way as the Planck CC and IRDC are most likely similar ISM structures in different observing conditions and probably in slightly different evolutionary stages. Both NHIE and HISA may be an intermediate phase between the diffuse cold neutral medium and star-forming molecular clumps represented by the Planck CC and IRDC.

Analysis of reflection effects in HS 2333+3927

The results of photometric and spectroscopic observations of the pre-cataclysmic variable HS 2333+3927, which is a HW Vir binary system, are analyzed. The parameters of the sdB subdwarf companion (Teff = 37 500 ± 500 K, log g = 5.7 ± 0.05) and the chemical composition of its atmosphere are refined using a spectrum of the binary system obtained at minimum brightness. Reflection effects can fully explain the observed brightness variations of HS 2333+3927, changes in the HI and HeI line profiles, and distortions of the radial-velocity curve of the primary star. A new method for determining the component-mass ratios in HW Vir binaries, based on their radial-velocity curves and models of irradiated atmospheres, is proposed. The set of parameters obtained for the binary components corresponds to models of horizontal-branch sdB subdwarfs and main-sequence stars.

The GALEX Arecibo SDSS Survey

We present the second data release from the GALEX Arecibo SDSS Survey (GASS), an ongoing large Arecibo program to measure the Hi properties for an unbiased sample of ~1000 galaxies with stellar masses greater than 1010 M⊙ and redshifts 0.025 < z < 0.05. GASS targets are selected from the Sloan Digital Sky Survey (SDSS) spectroscopic and Galaxy Evolution Explorer (GALEX) imaging surveys, and are observed until detected or until a gas mass fraction limit of a few per cent is reached. This second data installment includes new Arecibo observations of 240 galaxies, and marks the 50% of the complete survey. We present catalogs of the Hi, optical and ultraviolet parameters for these galaxies, and their Hi-line profiles. Having more than doubled the size of the sample since the first data release, we also revisit the main scaling relations of the Hi mass fraction with galaxy stellar mass, stellar mass surface density, concentration index, and NUV − r color, as well as the gas fraction plane introduced in our earlier work.

Thin discs, thick dwarfs and the effects of stellar feedback

Abstract We investigate the role of stellar mass in shaping the intrinsic thickness of galaxy discs by determining the probability distribution of apparent axial ratios (b/a) for two different samples that probe the faint end of the galaxy luminosity function. We find that the b/a distribution has a characteristic ‘U-shape’ and identify a limiting mass M*≈ 2 × 109M⊙ below which low-mass galaxies start to be systematically thicker. This tendency holds for very faint (MB∼−8) dwarfs in the local volume, which are essentially spheroidal systems. We argue that galaxy shape is the result of the complex interplay between mass, specific angular momentum and stellar feedback effects. Thus, the increasing importance of turbulent motions in lower mass galaxies leads to the formation of thicker systems, a result supported by the latest hydrodynamical simulations of dwarf galaxy formation and other theoretical expectations. We discuss several implications of this finding, including the formation of bars in faint galaxies, the deprojection of Hi line profiles and simulations of environmental effects on the dwarf galaxy population.

The circumstellar environment of the FS CMa star IRAS 00470+6429

AbstractFS CMa type stars are a recently described group of objects with the B[e] phenomenon that exhibit strong emission-line spectra and strong IR excesses. In this paper we report the first attempt for a detailed modeling of IRAS 00470+6429, for which we have the best set of observations. Our modeling is based on two key assumptions: the star has a main-sequence luminosity for its spectral type (B2) and that the circumstellar (CS) envelope is bimodal, composed of a slowly outflowing disk-like wind and a fast polar wind. Both outflows are assumed to be purely radial. We adopt a novel approach to describe the dust formation site in the wind that employs timescale arguments for grain condensation and a self-consistent solution for the dust destruction surface. With the above assumptions we were able to reproduce satisfactorily many observational properties of IRAS 00470+6429, including the HI line profiles and the overall shape of the spectral energy distribution.

Near-infraredH- andK-band studies of the 2006 outburst of the recurrent nova RS Ophiuchi

We present near-IR photo-spectroscopy in the H and K bands of the 2006 outburst of the recurrent nova RS Ophiuchi (RS Oph). The observations cover the period between 1 to 94 days after the eruption. The near IR light curve and an extensive set of spectra are presented, lines identified and the general characteristics of the spectra discussed. Analysis of the HI line profiles show the presence of broad wings on both flanks of a strong central component indicating the presence of a bipolar velocity flow in the ejecta. Such a flow is kinematically consistent with the bipolar structure that the object displays in high-resolution spatial images. We discuss the behaviour and origin of the Fe II lines at 1.6872 and 1.7414 micron and show that Lyman alpha and Lyman continuum fluorescence are viable mechanisms to excite these lines. We draw upon the result, that collisional excitation can also contribute in exciting and significantly enhancing the strength of these Fe II lines, to propose that these lines originate from a site of high particle density. Such a likely site could be the high-density, low temperature contact surface that should exist in the shockfront in between the shocked ejecta and red giant wind. Recombination analysis of the HI lines indicate deviations from Case B conditions during most of the span of our observations indicating optical depth effects. It appears likely that the breakout of the shockfront had not yet occured till the end of our observations. An analysis is made of the temporal evolution of the [Si VI] 1.9641 micron coronal line and another coronal line at 2.0894 micron which is attributed to [Mn XIV]. Assuming collisional effects to dominate in the hot coronal gas, estimates are made of the ion temperature in the gas.

The fundamental plane of dwarf irregular galaxies

Aims. Near-IR photometry of dwarf irregular galaxies (dIs) has been acquired to expand the sample of objects suitable for investigating the fundamental plane (FP) discovered previously by us. Data for blue compact dwarfs (BCDs), dwarf ellipticals (dEs), and dwarf spheroidal galaxies (dSphs) are amalgamated to evaluate how closely these classes of galaxies are related to dIs. Methods. Surface brightness profiles for dIs are modeled using a hyperbolic secant function (sech), which has been shown to sample the old galaxy component observed in the NIR (Ks). Also, profiles for BCDs are modeled using a sech function, but to this is added a Gaussian burst. Kinematics for dIs and BCDs are constrained by the width W20 of integrated HI line profiles, and motions within dEs and dSphs are judged from stellar velocity dispersions. Results. The existence of a FP for dIs is confirmed. Omitting extreme deviants, the scatter of dIs about the plane is 0.43 mag, somewhat higher than expected from observational errors alone. Corrections of line widths for tilt do not reduce the residuals, so motions must be predominantly random. Corrections of surface brightnesses for tilt have no effect either. BCDs and dEs lie precisely on the FP defined by dIs, suggesting strong underlying connections among dIs, BCDs, and dEs.

The Photometric and Kinematic Structure of Face‐on Disk Galaxies. I. Sample Definition, Hα Integral Field Spectroscopy, and H i Line Widths

We present a survey of the photometric and kinematic properties of 39 nearby, nearly face-on disk galaxies. Our approach exploits echelle-resolution integral-field spectroscopy of the H-alpha regions, obtained with DensePak on the WIYN 3.5m telescope Bench Spectrograph. This data is complemented by HI line-profiles observed with the Nancay radio telescope for 25 of these sample galaxies. Twelve additional line-widths are available for sample galaxies from the literature. In this paper, we introduce the goals of this survey, define the sample selection algorithm, and amass the integral field spectroscopic data and HI line-widths. We establish spatially-integrated H-alpha line-widths for the sample. We test the veracity of these spatially-integrated line profiles by convolving narrow-band imaging data with velocity field information for one of the sample galaxies, PGC 38268, and also by comparing to HI line profiles. We find HI and H-alpha line profiles to be similar in width but different in shape, indicating we are observing different spatial distributions of ionized and neutral gas in largely axisymmetric systems with flat outer rotation-curves. We also find vertical velocity dispersions of the ionized disk gas within several disk scale-lengths have a median value of 18 km/s and an 80% range of 12-26 km/s. This is only a factor of ~2 larger than what is observed for neutral atomic and molecular gas. With standard assumptions for intrinsic and thermal broadening for H-alpha, this translates into a factor of three range in turbulent velocities, between 8 and 25 km/s.

Circumstellar Atomic Hydrogen in Evolved Stars1

We present new results of a spectroscopic survey of circumstellar HI in the direction of evolved stars made with the Nancay Radiotelescope. The HI line at 21 cm has been detected in the circumstellar shells of a variety of evolved stars: AGB stars, oxygen-rich and carbon-rich, Semi-Regular and Miras, and Planetary Nebulae. The emissions are generally spatially resolved, i.e. larger than 4', indicating shell sizes of the order of 1 pc which opens the possibility to trace the history of mass loss over the past ~ 10^4-10^5 years. The line-profiles are sometimes composite. The individual components have generally a quasi-Gaussian shape; in particular they seldom show the double-horn profile that would be expected from the spatially resolved optically thin emission of a uniformly expanding shell. This probably implies that the expansion velocity decreases outwards in the external shells (0.1-1 pc) of these evolved stars. The HI line-profiles do not necessarily match those of the CO rotational lines. Furthermore, the centroid velocities do not always agree with those measured in the CO lines and/or the stellar radial velocities. The HI emissions may also be shifted in position with respect to the central stars. Without excluding the possibility of asymmetric mass ejection, we suggest that these two effects could also be related to a non-isotropic interaction with the local interstellar medium. HI was detected in emission towards several sources (rho Per, alpha Her, delta^2 Lyr, U CMi) that otherwise have not been detected in any radio lines. Conversely it was not detected in the two oxygen-rich stars with substantial mass-loss rate, NML Tau and WX Psc, possibly because these sources are young with hydrogen in molecular form, and/or because the temperature of the circumstellar HI gas is very low (< 5 K).

GMRTHI observations of the Eridanus group of galaxies

The GMRTHI 21 cm-line observations of galaxies in the Eridanus group are presented. The Eridanus group, at a distance of ≈ 23 Mpc, is a loose group of ≈200 galaxies. The group extends to more than 10 Mpc in projection. The velocity dispersion of the galaxies in the group is ≈240 km s−1. The galaxies are clustered into different sub-groups. The overall population mix of the group is 30% (E + S0) and 70% (Sp + Irr). The observations of 57 Eridanus galaxies were carried out with the GMRT for ≈ 200 h. HI emission was detected from 31 galaxies. The channel rms of ≈ 1 mJy beam−1 was achieved for most of the image-cubes made with 4 h of data. The corresponding HI column density sensitivity (3σ) is ≈ 1 × 1020 cm−2 for a velocity-width of ≈ 13.4 km s−1. The 3σ detection limit of HI mass is ≈ 1.2 X 107 Mpd for a line-width of 50 km s−1. Total HI images, HI velocity fields, global HI line profiles, HI mass surface densities, HI disk parameters and HI rotation curves are presented. The velocity fields are analysed separately for the approaching and the receding sides of the galaxies. These data will be used to study the HI and the radio continuum properties, the Tully-Fisher relations, the dark matter halos, and the kinematical and HI lopsidedness in galaxies.