Sample

by Tracy Halstead last modified Dec 19, 2011

The LITTLE THINGS sample includes 42 dwarf irregular (dIm) and Blue Compact Dwarf (BCD) galaxies. We obtained new VLA HI-line observations of 21 galaxies; the other 21 have data in the NRAO archives. (However, NGC 1156 was dropped from our sample because the archival observations did not have any line-free channels for determining continuum. Also, we obtained data on NGC 6822, but there is a zero-spacing issue and no maps are available with these data.) The galaxies are listed in Table 1 and the datasets in Table 2. The LITTLE THINGS sample was drawn from a larger multi-wavelength survey that includes 94 dIm, 24 BCDs, and 18 Sm galaxies (Hunter & Elmegreen 2004, 2006), the result of 15 years of observations. The HI sample covers a large range of dIm parameter space of the full survey (see Figure 1), including the extremes---from high star formation rate BCDs to low surface brightness dwarfs without any current star formation. Distances have been updated from those used by Hunter & Elmegreen (2004, 2006), and references for the new distances used here are given by Hunter et al. (in preparation).

Targets

aRH is the Holmberg radius, the radius of the galaxy at a B-band isophote, corrected for reddening, of 26.7 mag of one arcsec2.

bSFRD is the star formation rate, measured from Halpha, normalized to the pi×RD2, where RD is the disk scale length measured from V-band images. A galaxy without any detectable Halpha emission is listed as having a SFR of 0.

Data Sets

References for published datasets: Halpha images (Hunter & Elmegreen 2004); UBVJHK images (Hunter & Elmegreen 2006); Spitzer IRAC images (Hunter, Elmegreen, & Martin 2006); Spitzer IRS spectra (Hunter & Kaufman 2006, AJ, submitted); individual HI studies (Hunter, Elmegreen, & van Woerden 2001; Simpson, Hunter, & Knezek 2005; Simpson, Hunter, & Nordgren 2005; Kepley, Wilcots, Hunter, & Nordgren 2007).

Compare Props

Figure 1: Properties of the LITTLE THINGS HI sample (new observations [hashed +45° ]+archive [hashed -45°]) compared to the entire optical survey (open) of Hunter & Elmegreen (2004, 2006). The HI sample covers the range of parameters of the full survey. dIm and BCD galaxies have been combined. A star formation rate (SFR) of 0 is plotted as a log of -6. SFRD is the SFR normalized to pi×RD2, where RD is the disk scale length.