The Arecibo Galaxy Environment Survey VIII : Discovery of an Isolated Dwarf Galaxy in the Local Volume

The Arecibo Galaxy Environment Survey (AGES) has detected a nearby HI source at a heliocentric velocity of +363 km/s . The object was detected through its neutral hydrogen emission and has an obvious possible optical counterpart in Sloan Digital Sky Survey (SDSS) data (though it does not have an optical redshift measurement). We discuss three possible scenarios for the object : 1) It is within the Local Group, in which case its HI properties are comparable with recently discovered ultra-compact high velocity clouds; 2) It is just behind the Local Group, in which case its optical characteristics are similar to the newly discovered Leo P galaxy; 3) It is a blue compact dwarf galaxy within the local volume but not associated with the Local Group. We find the third possibility to be the most likely, based on distance estimates from the Tully-Fisher relation and its velocity relative to the Local Group.Comment: 5 pages, 6 figures, accepted for publication in MNRAS. Minor correction to institution and addres

The existence and detection of optically dark galaxies by 21cm surveys

One explanation for the disparity between Cold Dark Matter (CDM) predictions of galaxy numbers and observations could be that there are numerous dark galaxies in the Universe. These galaxies may still contain baryons, but no stars, and may be detectable in the 21cm line of atomic hydrogen. The results of surveys for such objects, and simulations that do/do not predict their existence, are controversial. In this paper we use an analytical model of galaxy formation, consistent with CDM, to firstly show that dark galaxies are certainly a prediction of the model. Secondly, we show that objects like VIRGOHI21, a dark galaxy candidate recently discovered by us, while rare are predicted by the model. Thirdly, we show that previous 'blind' HI surveys have placed few constraints on the existence of dark galaxies. This is because they have either lacked the sensitivity and/or velocity resolution or have not had the required detailed optical follow up. We look forward to new 21cm blind surveys (ALFALFA and AGES) using the Arecibo multi-beam instrument which should find large numbers of dark galaxies if they exist

The Arecibo Galaxy Environment Survey VII : A Dense Filament With Extremely Long HI Streams

We present completed observations of the NGC 7448 galaxy group and background volume as part of the blind neutral hydrogen Arecibo Galaxy Environment Survey (AGES). Our observations cover a region spanning 5x4 degrees, over a redshift range of approximately -2,000 < cz < 20,000 km/s. A total of 334 objects are detected, mostly in three overdensities at cz $\sim$7,500, cz $\sim$9,600 and cz $\sim$ 11,400 km/s. The galaxy density is extremely high (15 per square degree) and many ($\sim$24%) show signs of extended HI emission, including some features as much as 800 kpc in projected length. We describe the overall characteristics of this environment : kinematics, typical galaxy colours and mass to light ratios, and substructure. To aid in the cataloguing of this data set, we present a new FITS viewer (FRELLED : Fits Realtime Explorer of Low Latency in Every Dimension). This incorporates interactive source cataloguing tools which increase our source extraction speed by approximately a factor of 50.Comment: 15 pages, 13 figures, accepted for publication in MNRA

Attack of the Flying Snakes : Formation of Isolated HI Clouds By Fragmentation of Long Streams

The existence of long (> 100 kpc) HI streams and small (< 20 kpc) free-floating HI clouds is well-known. While the formation of the streams has been investigated extensively, and the isolated clouds are often purported to be interaction debris, little research has been done on the formation of optically dark HI clouds that are not part of a larger stream. One possibility is that such features result from the fragmentation of more extended streams, while another idea is that they are primordial, optically dark galaxies. We test the validity of the fragmentation scenario (via harassment) using numerical simulations. In order to compare our numerical models with observations, we present catalogues of both the known long HI streams (42 objects) and free-floating HI clouds suggested as dark galaxy candidates (51 objects). In particular, we investigate whether it is possible to form compact features with high velocity widths (> 100 km/s), similar to observed clouds which are otherwise intriguing dark galaxy candidates. We find that producing such features is possible but extremely unlikely, occurring no more than 0.2% of the time in our simulations. In contrast, we find that genuine dark galaxies could be extremely stable to harassment and remain detectable even after 5 Gyr in the cluster environment (with the important caveat that our simulations only explore harassment and do not yet include the intracluster medium, heating and cooling, or star formation). We also discuss the possibility that such objects could be the progenitors of recently discovered ultra diffuse galaxies.Comment: 46 pages, 27 figures, accepted for publication in MNRA

Substrate-Dependent Activation of Polyphenol Oxidase in Red Clover

Polyphenol oxidases (PPO) are copper metaloproteins that catalyse the oxidation of o-diphenols to quinones, highly reactive molecules which readily bind to nucleophilic sites on cellular components and proteins. Red clover protein, due to this enzyme is resistant to protease degradation during. Theses enzymes (circa. 60-65 kDa) are located in the thylakoid lumen and can be converted to a 40-45 kDa form by proteolysis both in vitro and in vivo (Gelder et al., 1997). Conversion to the smaller form has been demonstrated to confer activity at neutral pH. Other treatments, such as the presence of lipids or detergents eg. SDS, can also confer activity at pH7 (Gelder et al., 1997). Here we describe studies on treatments that affect red clover PPO activity at neutral pH, which is equivalent to the physiological pH of macerated/homogenised leaf extracts

The Arecibo Galaxy Environment Survey - X. The structure of halo gas around M33

As part of the H i Arecibo Galaxy Environment Survey (AGES), we have observed 5 × 4 deg of sky centred on M33, reaching a limiting column density of ∼1.5 × 1017 cm−2 (line width of 10 km s−1 and resolution 3.5 arcmin). We particularly investigate the absence of optically detected dwarf galaxies around M33, something that is contrary to galaxy formation models. We identify 22 discrete H i clouds, 11 of which are new detections. The number of objects detected and their internal velocity dispersion distribution is consistent with expectations from standard galaxy formation models. However, the issue remains open as to whether the observed velocity dispersions can be used as a measure of the H i clouds total mass, i.e. are the velocities indicative of virialized structures or have they been influenced by tidal interactions with other structures in the Local Group? We identify one particularly interesting H i cloud, AGESM33-31, that has many of the characteristics of H i distributed in the disc of a galaxy, yet there is no known optical counterpart associated with it. This object has a total H i mass of 1.22 × 107 M⊙ and a diameter of 18 kpc if at the distance of M33 (DM33 = 840 kpc). However, we also find that there are numerous other H i clouds in this region of sky that have very similar velocities and so it is plausible that all these clouds are actually associated with debris from the Magellanic stream