Probing the Density of "HI Monster" Galaxy Neighborhoods and Its Effect on Galaxy Growth

Presenter

Leyna Bajaj

Campus

UMass Amherst

Sponsor

Min Yun, Department of Astronomy, UMass Amherst

Schedule

Session 4, 2:30 PM - 3:15 PM [Schedule by Time][Poster Grid for Time/Location]

Location

Poster Board A16, Campus Center Auditorium, Row 1 (A1-A20) [Poster Location Map]

Abstract

In 2014 a population of 28 galaxies dubbed “HI Monsters'' were discovered by the Arecibo Observatory. As their name suggests, they contain some of the largest stockpiles of neutral hydrogen gas in our local universe (M_HI > 3 x 10¹⁰ M_⊙, which is ten times larger than that of our Galaxy ). The size of these reservoirs raises the question as to how they may have gotten so big. One proposed mechanism is that the flow and the duration of cold gas onto a galaxy may be environmentally dependent. For example galaxies that live in more crowded environments compete against the gravitational pull of their neighbors and capture less gas. Gravitational disruptions by neighbors may also hasten the conversion of gas into stars in the central parts. Thus the Monsters' large gas masses may be the result of their living in more isolated environments. Characterizing the density of the Monsters’ environments requires creating accurate maps of their neighborhoods. We use a tool to do this called the Extragalactic Distance Database (EDD) that logs the 3D positions of over 60,000 galaxies in the local universe. We run Voronoi tessellation and k-nearest neighbors algorithms on maps of the 10 Monsters in the database to determine their density. We compare each of these density distributions to a control sample of 94 randomly selected galaxies from the same database. In each case the density distributions of the Monsters are significantly different from the control group, confirmed by t-tests with p-values < 0.05. These results suggest the Monsters live in more isolated environments in agreement with the prediction from environmental impact on “cold flow”.

Keywords

galactic astronomy , galaxy environments, statistics

Research Area

Astronomy, Cosmology, and Astrophysics

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