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The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin
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The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

Apr 01, 2015

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Page 1: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

The extremely high gas content of galaxy UGC8802

Chang Rui-xiang

Hou Jin-liang

Shen Shi-yin

Page 2: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

• Understanding the content and distribution of cold gas in galaxies is an important step to understand the formation and evolution of galaxies.

• The GALEX Arecibo SDSS Survey (GASS):

to gather high quality HI-line spectra using the Arecibo radio telescope for ~1000 galaxies selected from SDSS and GALEX:

M* >1010M⊙

0.025 < z < 0.05

Page 3: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

Moran et al.(2010, ApJ, 720,1126)

Page 4: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

UGC8802 is an interesting target:

• z=0.0411

• M*=2*1010M ⊙

• HI mass: 2.1*1010M⊙

CO observations:

• H2 mass: 1.45*109M⊙

Long-slit spectroscopy: • SFR• D4000• metallicity

Moran et al.(2010, ApJ, 720,1126)

Page 5: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

Milky Way M31 UGC8802

Stellar mass (1010M⊙) 5.0 5.9~8.7 2

Disk scale-length (kpc) 2.3 4.8 5.8

HI mass (1010M⊙) 0.4 0.5 2.1

H2 mass (1010M⊙) 0.11 0.02~0.04 0.14

Gas fraction 0.09 0.08 0.5

Total SFR (M⊙ yr-1) 1~5 0.4~1.0 3.7

Abundance gradient

(dex kpc-1) -0.04~-0.07 -0.18~-0.027 -0.04

Page 6: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

The origin and the fate of the gas in UGC8802:

• Scenarios that the gas was acquired in a recent merging event are disfavored because of the regular kinematics of the disk.

• Further investigations are required to answer this question.

Our motivations:• to construct a simple model and test if the continuous ga

s-infall model can be viable for UGC8802• to further understand the origin and evolution of cold gas

in UGC8802

Page 7: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

Main assumptions of our model:

• The disk is sheet-like and composed by a set of independent rings.

• The disk origins and grows by continuous gas infall.• The radial profile of stellar mass surface density is expon

ential in the present day.

Page 8: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

Main ingredients of the model:

• gas infall rate:

• modified K-S star formation law:

• gas outflow rate:

22 2/)()(),( pttin erAtrf

),(),( trSFRbtrf outout

4.1)(),( gasrtr

free parameters: )(),( rrt p

Page 9: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

• Chang et al.(2010,ApJ,722,380) showed that later infall-peak time or lower SFE predicts bluer color, higher gas fraction, lower metallicity and higher SFR density.

• The predicted SFR surface density are more sensitive to the SFE.

• Our best-fitting model:

It is adopted that the infall-peak time increases while the SFE decreases from the inner disk to the outer parts

Page 10: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.
Page 11: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

The predicted evolution of gas surface density at three different Regions, 1rd (dot line), 3rd (solid line), and 5rd (dash line).

1rd

3rd

5rd

Page 12: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

• The model adopts late infall-peak time and low SFE in the outer disk results in high gas surface density in outer disk, which can explain the observed high gas fraction of UGC8802.

• Our results show that the continuous gas-infall model is also viable for UGC8802. This suggests that the cold gas in UGC8802 may be originated from continue gas-infall from the dark matter halo.

Page 13: The extremely high gas content of galaxy UGC8802 Chang Rui-xiang Hou Jin-liang Shen Shi-yin.

next steps:

• H2 mass: new star formation law