Probing the neutral gas reservoir with current and future HI galaxy surveys

Duffy et al. 2012

Michael G. Jones, Lourdes Verdes-Montenegro, Martha P. Haynes,

Riccardo Giovanelli, the ALFALFA Team, and the AMIGA Team

Sánchez-Ramírez et al. 2015

AMIGA • Study of the properties of ~1000 isolated galaxies.

• Observations in optical, NIR, FIR, Hα, CO, HI, and radio continuum.

• These galaxies appear to be almost “nurture free”.

Jones et al. 2017

Evolution in Compact Groups

HCG 44

20

´

Leisman et al. 2016 125 kpc

SDSS Image

ALFALFA HI map • They are thought to follow an

evolutionary sequence (Verdes-Montenegro et al. 2001), which can be tracked through their HI.

• Compact groups are small groups of galaxies that have number densities comparable to the centre of clusters (Hickson 1992).

A

B

C

D

ALFALFA Survey • The largest blind HI survey to date.

• Detected over 30,000 galaxies in HI.

• Maximum redshift only 0.06.

Leo P

The HI Mass Function • The HIMF is the intrinsic distribution of galaxy HI masses in the Universe.

• It is essentially a census of the galaxy population in atomic gas.

Jones et al. (submitted)

Low-mass slope

Knee mass

ALFALFA HI mass function

Bottom line: Cosmic variance still dominates the total uncertainty in the low-mass population.

Summary • All gas must go through the neutral phase between being accreted from

the ionised IGM and condensing to form molecular gas and stars.

• HI observations thus offer a unique and fundamental view of galaxies, and can act as an independent constraint on models of galaxy formation.

• Current HI surveys are necessarily much smaller in scale than optical surveys, which limits the our ability to perform a cosmologically fair census of low-mass galaxies.

• Current HI observations of individual galaxies do not have the combined sensitivity and resolution required to map their lowest column density gas.

• SKA will be capable of measuring the evolution of the HI content of the Universe over cosmic time and will allow us to map directly the accretion and stripping of gas from individual galaxies as they evolve.