1. z=0Modelling the atomic and molecular gas in galaxies and
comparisons with GASS and COLD GASS results
With Jian Fu, Qi Guo, Cheng Li, and the COLD GASS and GASS
teams

2. David
Schiminovich
(PI)
Barbara
Catinella

3. Amelie Saintonge

4. GALAXY SELECTION
a) Redshift range : 0.025 < z < 0.05
Motivation:
1) We want to detect HI and H2 down to levels of a few percent in
M(gas)/M* in about an hour of integration time.
2) We want to get an accurate estimate of the total cold gas mass with a single
pointing of both the Arecibo and IRAM telescopes.
b) Stellar mass range: log M* > 10
Motivation:
1) Span a range of stellar masses encompassing both “active” star-forming
galaxies and “passive” systems => quantify how the transition between these
two populations is reflected in their cold gas content. Avoid any selection on
morphology, environment etc.
2) In the mass range, all galaxies have roughly solar metallicity: conversion
factor from CO luminosity to H2 mass is simplified.
OBSERVING STRATEGY: Integrate until the galaxy is detected or a limiting
HI/H2 mass fraction ~1.5-3% is reached, i.e. Our survey will quantify the full
condensed baryon budget in these galaxies.

5. MILLENNIUM-II Simulations (Boylan-Kolchin et al 2009)

6. THE MERGING TREE

7. Models are based on the L-Galaxies Code developed
by Springel, Croton, De Lucia, Guo et al.

8. Radially Resolved Models for Galactic
Disk Formation
Scale radius of the infalling gas is proportional to λ Rvir (following Fall &
Efstathioiu 1980; Mo, Mao, White 1998)
The gas that falls is at one snapshot is simply superposed on the gas that
has already fallen in at earlier times.

9. Krumholz, McKee and Tumlinson 2009 Blitz & Rosolowsky 2004,2006

10. Comparison of Model
Profiles with THINGS/
HERACLES data from Bigiel
et al 2008
GAS PROFILES ARE TOO FLAT
AND THE MOLECULAR GAS IS
RAPIDLY CONSUMED IN THE
INNER DISK.
PROBLEM CANNOT BE SOLVED
BY ADJUSTING FREE
PARAMETERS.

11. Comparison of Model
Profiles with THINGS/
HERACLES data from Bigiel
et al 2008
IF ENERGY FROM SUPERNOVA
IS MORE EFFICIENTLY
DISSIPATED IN DENSE INNER
REGIONS OF THE DISK (i.e. LESS
COLD GAS IS REHEATED ), THEN
MODELS CAN FIT DATA.
Caveat: Radial
inflow of gas has not
been considered

12. The Models Provide a Reasonable Match to the Observed
Mass Functions of HI, H2 and Stars in the Local Universe

13. It is interesting to consider the global scaling relations between stellar mass,
stomic gas mass and molecular gas mass for an ensemble of disk galaxies

14. What Are the Physical Drivers of these Scaling Relations?
1) The MASS OF THE DARK MATTER HALO determines the mass of
baryons that is able to cool. Because supernovae feedback is less efficient in
massive halos, a larger fraction of the baryons that cool are converted into stars.

15. What Are the Physical Drivers of these Scaling Relations?
1) The SPIN PARAMETER sets the contraction factor of the infalling gas.
A higher spin parameter results in larger galaxies with lower gas surface
densities.

16. What Are the Physical Drivers of these Scaling Relations?
1) The FRACTION OF GAS in the galaxy that was ACCRETED recently
(i.e. Gas that has has less time to be turned into stars).

17. COMPARE WITH DR2
FROM THE
COLD GASS SURVEY
(300 galaxoes with both HI
observations from Arecibo and CO 1-0
observations from the IRAM 30m
telescope)

18. BLUE: Arecibo/IRAM detections RED: Arecibo/IRAM non-detections

19. PROCEDURE:
1) Analyze detections and non-detections separately.
2) Analysis of population of galaxies with detected HI/CO
allows us to test the disk formation models .
3) Analysis of galaxies without detected gas allows us to
test whether “quenching” processes (in particular
radio-mode AGN feedback) operates the same way in the
models and in the data.

20. Comparison of Mean HI and H2 scaling relations
Atomic Gas Molecular Gas

21. Saintonge et al 2011
Molecular gas depletion times are shorter in more actively star-
forming galaxies

22. Distribution Functions of the HI detections in bins of
mass, stellar mass density, concentration

23. Trends in non-detected fraction do NOT agree with the
models
Fraction of non-
detections is
independent of
stellar mass in the
data, but depends
strongly on stellar
surface density and
concentration (i.e.
Bulge-to-disk ratio)

24. In the models, “radio-mode” AGN feedback prevents gas
from cooling in massive galaxies (with black holes) located in
halos above ~10^11 M_sun. Observationally, this is
manifested as a strong threshold in STELLAR MASS

25. H2 detections and non-detections in 2-dimensional
planes of stellar mass and galaxy structural parameters

26. Natural interpretation of the results: processes
associated with the formation of galactic bulges and
or black holes are most directly responsible for shutting
down star formation in galaxies.

27. PHOTOMETRIC INDICATORS OF
ATOMIC GAS CONTENT

28. UGC 8802: A Case Study of a Star-Forming Outlier
from the HI “plane”, with unusually high HI fraction
M(HI) = 2 x 10 10 M_sol
Moran et al 2010

29. As the HI gas fraction increases, galaxies become bluer on the outside relative
to the inside. This effect is weaker in control samples matched in stellar mass,
structural parameters and specific star formation rate.
Wang et al 2011

30. Preliminary work with Cheng Li:
Find best photometric “predictors” of the HI content of a galaxy
Update of HI gas
fraction “plane” to
include a colour
gradient term --
gives much more
accurate predictions
for high Hi fraction
galaxies.

31. GASS-SDSS cross-correlation functions:
“real” versus “predicted”
What is this useful for? Creating mock catalogues –
tuning up future surveys with real data!