1. The Effect of HI Gas on Star Formation of Nearby Galaxies
Zhou Zhimin (周志民)
(NAOC)

2. HI is a good tracer of galaxy interactions.
Processes determining the evolution of gas in discs of galaxies.
Zasov & Zaitseva 2017 (arXiv: )
A flow chart of the evolution of an individual galaxy. The galaxy is represented by the dashed box which contains hot gas, cold gas, stars and a supermassive black hole (SMBH). Gas cooling converts hot gas into cold gas, star formation converts cold gas into stars, and dying stars inject energy, metals and gas into the gas components. In addition, the SMBH can accrete gas (both hot and cold) as well as stars, producing AGN activity which can release vast amounts of energy which affect primarily the gaseous components of the galaxy. Note that in general the box will not be closed: gas can be added to the system through accretion from the intergalactic medium and can escape the galaxy through outflows driven by feedback from the stars and/or the SMBH. Finally, a galaxy may merge or interact with another galaxy, causing a significant boost or suppression of all these processes.
HI is a good tracer of galaxy interactions.
Hi disk of a galaxy is relatively diuse and usually a few times more extended than the stellar disk, which means it can be very easily disturbed by external forces.
spiral galaxies in high density environments (galaxy clusters) tend to have on average, less neutral hydrogen (H i) than galaxies of the same type and size in the field. (Chung et al. 2009, Fabello et al. 2012, Denes et al. 2015)
HI in galaxies traces the fuel for future star formation.
H. Mo, F. van den Bosch & S. White 2010

3. Gas – galaxy scaling relations
Kennicutt-Schmidt Law:
Star formation Density
Kennicutt 1998, ApJ, 498, 541
Gas Surface Density
Kennicutt 1998, ApJ, 498, 541

4. Gas – galaxy scaling relations
Gas fraction correlates with colors (g-r, NUV-r), stellar mass, SSFR. (Kannappan 2004, Zhang et al. 2009, Catinella et al. 2010, Huang et al. 2012, Li et al. 2012)
Photometric estimators of HI fraction
Huang et al. 2012

5. The present HI projects :
GASS: ~1000 galaxies with Stellar mass >10^10 Msun
HIghMass: Hi massive (M_Hi > 10^10Msun ) and high gas fractions
SHIELD: Survey of Hi in Extremely Low mass Dwarfs
α.40–SDSS–GALEX sample: Huang et al. 2012
Ha^3: Hα imaging survey of HI selected galaxies from ALFALFA; Virgo & Coma clusters
What we need:
identify which galaxy properties that are causally connected with HI content
How HI gas affect star formation of galaxy
A complete HI-detected sample and HI-undetected sample
Accurate measurement for SFR and stellar mass of galaxies

6. Arecibo Legacy Fast ALFA survey (ALFALFA)
a blind 21-cm (L-band, 1.4 GHz) survey, which covers 7000 deg2 and has detected 30,000 galaxies out to z = (Giovanelli et al. 2005; Haynes et al. 2011).
high galactic latitudes with -2 < Decl. < +38

7. Sample & Data HI-detected complete sample in 15 deg^2
Sample No.：70
RA: 11h-11.5h, DEC: 9-11deg
Compared sample in the same region:
Optical selected from SDSS MPA DR7 (mag_r<17.7)
Undetected by ALFALFA HI: 110

8. Observation for HI sample: Ha narrow-band imaging
BFOSC/YFOSC on 2.16/2.4m
Exptime: R:3～10min, Hα: 10~30min
Observation date: (2.16,LAM)、 (2.16,ZHOU)、 (2.4,ZHOU)
continuum-subtracted Ha images (top) & stellar continuum images (bottom)

9. Estimate SFR & stellar mass for HI-detected galaxies:
Ha+12um  SFR (Wen et al. 2014)
WISE 3.6um  stellar mass (Wen et al. 2013)

10. Comparing physical properties of HI-detected & -undetected samples
redshift

11. Color u-r
Stellar mass
SSFR
SFR

12. Surface SFR Surface Stellar mass R90/R50
Compared with HI-undetected sample, HI-detected galaxies are/have:
bluer (2.27 vs 2.51)
higher SFR (-0.28 vs -0.76) and surface density (-2.02 vs -2.24)
higher SSFR (-0.71 vs -1.61)
Similar stellar mass BUT lower surface density (7.69 vs 8.36)
lower concentration (2.27 vs 2.51)
SFR: vs -0.76; Sig_SFR: vs -2.24
GM: 9.48 vs 9.85 (9.73 vs 9.86); Sig_GM: 7.69 vs 8.36
SSFR: vs -1.61; color: 1.68 vs 2.08
Conc: 2.27 vs 2.51
R90/R50

13. There are different slops in the stellar mass-SSFR relation!
SF MS
slop=-0.33
slop=-1.08 QC
HI-detected galaxies are located on SF main sequence, but HI-undetected ones are in quenched cloud.
There are different slops in the stellar mass-SSFR relation!
HI-detected: for all sample, for z>0.025
HI-undetected: -1.08
There are overlaps (or similar properties ) between HI-detected and –undetected samples.

14. The relation between HI, SF, and M*
There are tight relations for HI-SFR and f_HI – SSFR;
The relations still exist for galaxies with the same stellar mass.

15. The relations between HI size and galaxy size
D_HI defined at HI surface density of 1 Msun pc−2 (Broeils & Rhee 1997)
R_HI=(6.2±2.8) x Re,r
R_HI=(5.8±3.2) x Re,Ha

16. Concentration Asymmetry Smoothness HI gas fraction vs morphology indexHa
Concentration Asymmetry Smoothness
galaxy mass R
HI gas fraction vs morphology index
NO obvious correlation between HI fraction and galaxy stellar and SF distribution.

17. Conclusions
Compared with HI-undetected sample, HI-detected galaxies have more active star formation, and are located on SF main sequence.
There are different slops in the stellar mass-SSFR relation for HI-detected and -undetected galaxies.
There are overlaps between the two samples.
There are tight relations for HI-SFR and f_HI – SSFR, even for the galaxies with the same stellar mass.
There are no obvious correlations between HI fraction and galaxy stellar and SF distribution.
The HI size is ~6 times of that of galaxy stellar and star formation.

18. Next … IC 676, S0 RA = 168.1658 DEC= 9.0562 Nucleus 2 Nucleus 1 HST
DECaLS
HST

19. Erwin & Sparke 2003

20. Alatalo et al. (2013) CO data from ATLAS3D CARMA Log10 H2=8.71 Msun
CARMA ATLAS3D CO survey of ETGs

21. IFU Data from ATLAS3D with SAURON

22. Thanks Further Discussion Is the HI gas consumed by the central SF?
IC 676 has similar SFR to the galaxies with similar stellar mass, but much lower HI fraction, or much higher SFE.
Is the HI gas consumed by the central SF?
How doses the double nuclei form?
Which mechanism promotes this process?
Internal structure (bar) or galaxy interaction ?
Thanks

23. Can u band trace Star Formation rate? SCUSS u band as SFR tracer

24. Why use u band to trace SFR?
Advantage in u band:
a substantial contribution of light from young, massive stars.
in the absence of UV measurements the u band luminosity may be used instead as an SFR indicator (Cram 1998)
u band data have high spatial resolution and are more easier achieved.
New surveys: CFHTLS、PS1、SCUSS、LSST provide u band data with high quality.
u 波段

25. Disadvantage:
The main disadvantage of using UV/optical luminosities as tracers of the SFR is their sensitivity to dust attenuation.
the geometry of dust with respect to the stars can lead to different color excesses, E(B−V), between the ionized gas and the stellar continuum. (Shivaei et al. 2015)
the color-excess is 2.27 times larger for the nebular emission lines than for the stellar continuum.
E(B-V)stellar=0.44 E(B-V)gas (Calzetti et al. 2000)
large numbers of relatively old stars that also contribute to the actual U -band luminosity of disk galaxies. (Cram 1998)
For u -band luminosities, however, it is somewhat more difficult to assign a simple scaling factor to derive an SFR as a result of the strong dependence on the evolutionary timescale (Hopkins et al. 2003).

26. Data
WISE
SCUSS
SDSS

27. Results Ha Ha
12um
22um

28. u+IR vs Ha
Zhou et al. (2017, ApJ, 835, 70)

29. Summary We calibrate u/u+12um/u+22um to SFR (Ha)
u band can be used as a SFR tracer when accuracy request is not high ( dex).
its sensitivity to dust reddening and SFH.
larger samples of intermediate- and high z galaxies are needed to test the applicability.
It can be used in the future survey and sample (ELG) selection.

30. Thanks Again!