Environmental Effects on the Star Formation History of Galaxies
Wen Shi, Cheng Li (Tsinghua University)
Division of Particle and Astrophysical Science, Nagoya University
Background and Purpose

Lots of observations and theories have led to a so-called “inside-out quenching process” for galaxies, in which a galaxy evolves from “blue” galaxies (star-forming, withno/little bulge) into “red” galaxies (little star formation, perhaps with a dense bulge) with star formation extinguishment expanding from galaxy center to the edge.
However, the underlying physical process is uncertain yet. There’re various channels causing star formation quench like halo quenching, morphology quenching and so on. Inparticular, the halo quenching process is quite different for central and satellite galaxies. Therefore, central/satellite division becomes crucial when we’re discussing quenchingprocess. The same logic applies to other environmental parameters, so we’ll need to examine their influence on galaxy quenching. And this helps to understand the “natural” or“mature” scenario of galaxy evolution.

Data and Method
MaNGA data:

The MaNGA MPL-6 datacube provides us with spatially resolved spectrum inwavelength 3600 to 10000 Å for 4621 individual galaxies. Then spectral fitting with
PPXF method (Cappellari & Emsellem, 2004; Cappellari, 2017) is applied to every
spaxel to obtain a 2D distribution of the star formation indicators we need.

Indicators from MPL-6:( X / X)
4000 Å break at galaxy center and Re (effective raidus) (Balogh et al. 1999)( X )−Dα(D( X))≡D
f (1.5 X): (mass-weighted) fraction of quenched spaxel within 1.5Re(4000), X(())∗ ×<1.5 Xf (1.5 X) =(4000),X() =Environmental Parameters:

1,<1.5 X∗(4000) > 1.60,XℎX

X(GyX) < 2.0

Halo mass

A halo-based group catalog for SDSS DR13Virial radius(Lim, S. H., et al. 2017, Mon Not R Astron Soc, 470, 2982)

Central/Satellite division

ELUCID applied to SDSS DR7(Wang, H., et al. 2014, Astrophys J, 794)

local density log(within 1 Mpc)

large scale structure (LSS) type

Results and Analysis
1) Cen/Sat division
Red, Totally Quenched, TQ- f (1.5 X) > 0.9；
Green, Partially Quenched, PQ- 0.1 < f (1.5 X) ≤ 0.9；
Blue, Star Forming, SF- f (1.5 X) ≤ 0.1;
（Wang et al. 2018）

Fig. 1 - D( X)-D( X ), different mass, cen/sat galaxies( X)-D( X ) plot
In Fig. 1, The distribution of galaxy on the Dstrongly depends on mass, which is discussed in detail in Wang, E., et al. 2018,Astrophys J, 856, 137. In the same mass range, cen/sat division won’t influence theirposition on the subplot.

Fig. 3 - Average D( X / X)/α(D)-log ( ), different mass—— all the galaxies；··· satellite galaxies；—·— central galaxies

The situation is exactly thesame for D( X). But alpha isstill unaffected.
(Although there might be someslight trend in the low mass case, it's
within the error range of D)

In Fig. 4 (Shortly speaking, thefive bars of the same color in thesame subplot add up to 1), thefraction of TQ galaxies becomesbigger than SF galaxies when local
density increases. This phenomenon
occurs in cluster galaxies.
Fig. 4 - Fraction of #galaxies in different density bin, different mass & LSS type3) d/r200: distance to center/virial radius of halo (for satellite galaxies only)
Fig. 2 - Average D( X / X)/α(D)-log∗/

In Fig. 5, the parameters seem not
influenced by distance. The reason could bevarious. It can be because the quenchingprocess simply has nothing to do with theradius, or because we have too few satellite
galaxies to make further division. Projection
reason also counts. Any way, further
investigation or discussion is needed.

⊙ , cen/sat galaxies

In Fig. 2, when stellar mass is low, average D4000 is higher for satellite thancentral galaxies. But when mass goes up, the difference between central and satellite
galaxy become vague, both d4000 at center or Re.
What about (), which stands for the “gradiant” of? In the rightpanel of Fig. 2, we can find () have nothing to do with cen/sat division！
So we claim:① Cen/sat division will influence the development of “inside-out quenching” forindividual galaxies: low mass satellites tend to evolve further into TQs② However, galaxies of the same mass have same “quenching route”: cen/sat( X)division will NOT affect galaxies' deviation from 1:1 relation on the D( X ) plot.
D2) Local Density / Halo Mass & LSS (large scale structure) type

Since local density and halo mass originally have very strong connection toeach other, it's not surprising that they give almost the same conclusion. We've only
displayed plots for local density here.
In Fig. 3, in the same line (mass range), D( X ) goes up with local density,
especially for low mass galaxies, and this trend disappears in the high mass region.
What’s more, for lines of the same mass, satellite galaxies react more
intensively to local density increasement than central galaxies. This is consistent withour conclusion for cen/sat division.

Fig. 5 - DConclusion( X / X)/α(D)- /, different mass1) α(D) in galaxies ONLY depends on stellar mass; all the environmental factors wementioned above affect galaxy center and edge SYNCHRONOUSLY.
2) low-mass satellite galaxies can develop faster into TQ galaxies, compared with centralgalaxies in the same mass range; and this difference disappears when mass increases.
3) In environments with high local density/halo mass, fraction of TQ galaxies are higher
for low-mass galaxies; this pattern is only seen in cluster galaxies.
4) We didn’t find influence of /for satellite galaxies.