HIperEdge - An HI perspective on environment driven galaxy evolution

HIperEdge - An HI Perspective on Environment-Driven Galaxy Evolution

Members of the Team:

PI: Marc Verheijen

Danielle Lucero (PD): HI in early-type galaxies
Anastasia Ponomareva (PD): TF relations, HI rotation curves and mass models
Kyle Oman (PD): Observing simulations
Avanti Gogate (PhD): HI properties and local cosmic environments (nurture)
Pooja Bilimogga (PhD): HI properties and global cosmic environments (nature)
Julia Healy (PhD): HIMF and Omega_HI from stacking in different environments
Tirna Deb (PhD): HI properties of galaxies in cluster infall regions
Robin Kooistra (PhD): Hunting HI filaments in galaxy surveys


The well-known morphology-density relation is a clear manifestation of the notion that the cosmic environment of galaxies influences their structural properties and star formation activity, both during a galaxy's formation process (nature) as well as during is subsequent evolution and interaction with its environment (nurture).  A variety of physical mechanisms affect the growth and shaping of galaxies such as accretion, merging, tidal disruptions and ram-ressure stripping.  The distribution and kinematics of the atomic hydrogen in and around galaxies plays an important role in these processes, not only intrinsically as the fuel of star formation and as an agent of dynamical instabilities, but also as a tracer of extrinsic processes that induce asymmetries, tidal tails and ram-pressure filaments.

The goal of HIperEdge is to obtain an HI perspective on the Morphology-Density relation by studying the spatially resolved morphologies and kinematics of the HI gas in galaxies over a range of local and global cosmic environments, thereby revealing the importance and dominance of the various physical mechanism that (re)shape galaxies since their epoch of formation.  In particular, HIperEdge aims as measuring the sizes and column-density distributions of HI disks, as well as the frequency of asymmetries, warps, tidal features, mergers and ram-pressure remnants in different cosmic environments, ranging from voids to galaxy groups to the outskirts of galaxy clusters.

Observationally, such a study requires three important attributes.  First of all, it requires an adequate column-density sensitivity to map the outskirts of the HI disks that are most easily influenced by tidal forces and the inter-galactic medium.  Based on existing observations of intergalactic HI filaments, a column-density sensitivity of 5x1019 [cm-2] should be achieved.  Second, a sufficiently large volume should be surveyed to obtain adequate statistics and sufficiently large samples of galaxies drawn from different cosmic environments, whereby the statistical uncertainties are not dominated by sample variance.  This volume should be surveyed at a sufficient linear resolution to properly resolve the HI features of interest.  Third, there should be a significant amount of ancillary photometric and spectroscopic data available to characterize the optical morphologies, the evolutionary state of the stellar populations and the physical state of the inter-stellar medium of galaxies that have been observed in HI.

A medium-deep survey with Apertif at its highest angular resolution, covering roughly 300 deg^2 distributed over various areas on the sky and coordinated with surveys at other wavelength regimes, would be adequate to meet the abovementioned observational requirements.

Another important goal of HiperEdge is to compare the observational findings from the Apertif medium-deep survey with the results from cosmological hydrodynamical simulations of galaxy and structure formation.  By providing observational constraints, it will contribute to a better understanding and implementation of the physical mechanisms that operate within these simulations.

The HiperEdge team consists of 3 postdocs and 3 PhD students who are focusing on various aspects of the project such as source finding and characterization, quantifying cosmic environments, and observing computer simulations.  They are embedded within a broader collaboration with astronomers at the Kapteyn Institute, ASTRON and other institutes around the globe.

Figure caption: Three examples of HI features that signify physical processes that affect the evolution of galaxies.  Left: extraplanar gas in NGC 891 indicating a strong galactic fountain and possibly accretion of gas from a nearby companion.  Middle: A tidal feature associated with the lenticular galaxy NGC 4111 embedded in a small group of galaxies in Ursa Major.  Right: A HI filament as a result of ram-pressure stripping in the Virgo cluster.  The orange contours indicate a column-density of 5x10^19 [cm^-2], a sensitivity necessary to reveal these features. 

Design: Kuenst.    Development: Dripl.    © 2020 ASTRON