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In order to investigate the contribution of diffuse components to their total HI emission, we have obtained high precision HI line flux densities with the 100m Green Bank Telescope for a sample of 100 isolated spiral and irregular galaxies which we have previously observed with the 43m telescope. A comparison of the observed HI line fluxes obtained with the two different telescopes, characterized by half-power beam widths of 9 arcmin and 21 arcmin respectively, exploits a ``beam matching technique to yield a statistical determination of the occurrence of diffuse HI components in their disks. A simple model of the HI distribution within a galaxy well describes ~75 % of the sample and accounts for all of the HI line flux density. The remaining galaxies are approximately evenly divided into two categories: ones which appear to possess a significantly more extensive HI distribution than the model predicts, and ones for which the HI distribution is more centrally concentrated than predicted. Examples of both extremes can be found in the literature but little attention has been paid to the centrally concentrated HI systems. Our sample has demonstrated that galaxies do not commonly possess extended regions of low surface brightness HI gas which is not accounted for by our current understanding of the structure of HI disks. Eight HI-rich companions to the target objects are identified, and a set of extragalactic HI line flux density calibrators is presented.
We report on the results of radio observations in the 21 cm emission line of atomic hydrogen (HI) of four relatively isolated ultra-diffuse galaxies (UDGs): DGSAT I, R-127-1, M-161-1, and SECCO-dI-2. Our Effelsberg observations resulted in non-detect
In this short write-up, I will concentrate on a few topics of interest. In the 1970s I found very extended HI disks in galaxies such as NGC 5055 and NGC 2841, out to 2 - 2.5 times the Holmberg radius. Since these galaxies are warped, a tilted ring mo
We use the textsc{Romulus25} cosmological simulation volume to identify the largest-ever simulated sample of {it field} ultra-diffuse galaxies (UDGs). At $z=0$, we find that isolated UDGs have average star formation rates, colors, and virial masses f
We have obtained imaging data in two photometric bands, g and r, for a sample of 42 isolated lenticular galaxies with the Las Cumbres Observatory one-meter telescope network. We have analyzed the structure of their large-scale stellar disks. The para
Studying the atomic gas (HI) properties of the most isolated galaxies is essential to quantify the effect that the environment exerts on this sensitive component of the interstellar medium. We observed and compiled HI data for a well defined sample o