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

Abstract

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 galaxies. The FIGGS galaxies represent the extremely low mass end of the dwarf irregular galaxies population, with a median M B ∼ −13.0 and median H I mass of ∼3 × 10 7 M , extending the baseline in mass and luminosity space for a comparative study of galaxy properties. The H I data are supplemented with observations at other wavelengths. In addition, distances accurate to ∼10 per cent are available for most of the sample galaxies. This paper gives an introduction to FIGGS, describes the GMRT observations and presents the first results from the H I observations. From the FIGGS data, we confirm the trend of increasing H I to optical diameter ratio with decreasing optical luminosity; the median ratio of D H I /D Ho for the FIGGS sample is 2.4. Further, on comparing our data with aperture synthesis surveys of bright spirals, we find at best marginal evidence for a decrease in average surface density with decreasing H I mass. To a good approximation, the discs of gas-rich galaxies, ranging over three orders of magnitude in H I mass, can be described as being drawn from a family with fixed H I average surface density.

Star Forming Dwarf Galaxies

“…H I masses range from a few 10 6 M at M B ∼ -10 (represented in the FIGGS sample) up to a few times 10 9 M at M B ∼-20. The relative H I mass fraction varies from about 5% of the dynamical mass at the high mass end to almost 100% at the low mass end [4,142]. The H I disk thickness increases with decreasing luminosity, reaching a mean axis ratio of < q >∼0.6 in the faintest dI galaxies [136].…”

“…SFR ∝ Σ 1. 4 g , where Σ g is the gas surface mass density. As a first approximation one may interpret this relation if the SFR is a product between the surface mass density and the collapse time of a supermassive molecular cloud.…”

“…The sample has been collected from various publications [4,13,37,50,63,95,129,137,161,Bergvall et al,unpublished]. The classification is therefore not homogeneous and the sample is not in any sense complete.…”

“…A dedicated Spitzer programme, the Spitzer Local Volume Legacy Syrvey (LVL) has observed 258 nearby galaxies, many of which are supplemented by groundbased images in broadbands and Hα. The Faint Irregular Galaxies (65 dIs) GMRT Survey [FIGGS;4], is using the Giant Metrewave Radio Telescope (GMRT) to perform volume limited (<10Mpc) H I observations of SFDGs. The H I Nearby Galaxy Survey [THINGS;163], at the VLA, includes 34 galaxies, of which about a dozen are SFDGs, in the distance interval 3<D<15 Mpc.…”

Cold H i in faint dwarf galaxies

“…The sample of galaxies we use is drawn from the Faint Irregular Galaxy GMRT Survey (FIGGS) (Begum et al 2008), and FIGGS2 survey (Patra et al 2015 (submitted)). These two samples contain a total of 73 galaxies with HI interferometric images.…”