The Spitzer Survey of Stellar Structure in Galaxies (S4G)

Overview Volume-limited (D<40Mpc, 𝑉 𝑟𝑎𝑑𝑖𝑜 <40𝑘𝑚× 𝑠 −1 ) Size-limited ( 𝐷 25 >1′) Magnitude-limited ( 𝑚 𝐵𝑐𝑜𝑟𝑟 <15.5) 2352 nearby galaxy 3.6 and 4.5 µm with IRAC(Infrared Array Camera) pixel size 0.75" spatial resolution ∼100 pc. surface-brightness limit(3.6𝜇𝑚): ∼27 𝑚𝑎𝑔 arcsec −2

3.6 and 4.5 µm band Best tracers of stellar mass image the Rayleigh-Jeans limit of the blackbody emission for stars with T > 2000 K. mid-infrared (3.6–4.5) color in nearby galaxies is nearly constant with radius and is independent of the age of the stellar population and its mass function a very weak 3.3 μm PAH feature, Hot dust (Td > 500 K) co-adding them, improve the signal-to-noise ratio (S/N)

Pipeline P1: Takes the raw basic calibrated data FITS P2: creates a mask for the foreground and background objects for each of the individual galaxies. P3: measures the standard global galaxy properties such as size, axial ratio, magnitude, color, etc., and computes the radial profiles of the standard properties. P4: deconstructs each galaxy into its major structural components. P5: application of the ICA method to separate the light from old stars and dust.

P4 Bulge+disk+bar +nuclear ring +nuclear point source

P5 ICA (independent Component Analysis) Old stars (age t ~ 2–12Gyr) have colors in the range -0.2 < [3.6]-[4.5]< 0, whereas dust corresponds to [3.6]-[4.5]> 0, and this difference in SED allows ICA to separate both components.

Science The Faint Outskirts of Galaxies Bulges: Classical, Disk-like, Boxy/Peanut Bars Galactic Rings Spiral Arms Early-Type Galaxies and Dwarfs

S4G MORPHOLOGY Buta+15 present classifications of S4G: CVRHS the stage, E-S0-S-I position along a modified Hubble sequence the family, SA(nonbarred)-SAB-SB(barred) the variety, r(closed inner ring)-rs-s(open spiral) outer ring classification, R(closed outer ring)- R’(outer pseudoring made of variable pitch angle outer spiral arms) Others, lense, nuclear ring(lense, or bar), etc.

Break and truncation Break: 82%, 7.9 ± 0.9 kpc. Truncations: 20/34, 34 highly inclined spiral galaxies in SDSS and S4G Surface-brightness profiles in SDSS band and 3.6𝜇𝑚 color and stellar surface mass density profiles Break: 82%, 7.9 ± 0.9 kpc. Truncations: 20/34, 14 ± 2 kpc, mass density profile

Strong correlations exist between the truncation radius and the maximum rotational velocity and the specific angular momentum of the disc. breaks are more likely a phenomenon related to a star-formation threshold truncations have a strong connection with the maximum angular momentum of the galaxy.

thick disk, thin disk two stellar and one gaseous isothermal coupled disks in equilibrium

mass-to-light ratio (Υ) Υ T / Υ 𝑡 =2.4 and Υ T / Υ 𝑡 =1.2 (different SFH) radial bins: 0.2 𝑟 25 < |R| < 0.5 𝑟 25 and 0.5 𝑟 25 < |R| < 0.8

Result 𝑀 𝑇 / 𝑀 𝑡 1/3-2 for Υ T / Υ 𝑡 =1.2 thick disks are much more massive than generally assumed(fitting function)

thick disks do not flare significantly within the observed range in galactocentric radii the ratio of thick-to-thin disk scale heights is higher for galaxies of earlier types

Thick disk Formation First, a thick stellar disk is created during and soon after the buildup of the galaxy by the stirring action from massive disk clumps and the instabilities that form those clumps. A thin disk subsequently forms from gas which has not initially been spent in stars, and from gas that arrives later at a lower rate so that, when combined with the hot disk and bulge that are already present, it is relatively stable and cannot heat itself much. The newly accreted gas makes the thick disk scale height, 𝑍 𝑇 , shrink, and if this shrinkage is a relatively small amount, then the final thick disk remains a distinct component of the galaxy, with a younger thin disk inside of it. In the case of thick-disk-dominated galaxies, the thick disk forms partly at high redshift by internal disk stirring, as above, and then increases its mass over a Hubble time by the heating of the thin disk by internal disk substructure, such as large star clusters and GMCs, and the accretion of satellite galaxies.

NGC 4244 The late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick disk. Two disk components, whose identification can only be done in the near side of the galaxy. We argue that the subtlety of the thick disk is a consequence of either a limited secular evolution in NGC 4244, a small fraction of stellar material in the fragments which built the galaxy, or a high amount of gaseous.

NGC 4013 :UNUSUAL VERTICAL MASS DISTRIBUTION three stellar flattened components (thin+thick disk plus an extra and more extended component) and one gaseous disk.

extended component The EC has a longer scale length than the galaxy disks, is smooth, and its properties do not depend strongly on varying galactocentric radii. We favor a scenario in which the EC was formed in a two-stage process, in which an initially thick disk was dynamically heated by a merger soon enough in the galaxy history to have a new thick disk formed within it.

Break in thin and thick disk Sample: 70 edga-on galaxy −3≤𝑇<8 Truncation Antitruncation

thin disks often truncate (77%). Thick disks truncate less often (31%), but their break radius is comparable with that in the thin disk. One of dynamical origin affecting both disks simultaneously and another one only affecting the thin disk a single mechanism that creates a truncation in one disk or in both depending on some galaxy property. Thin disks apparently antitruncate in around 40% of galaxies.

ETG with debris Sample: 11 ETG (T<0) with tidal debris from 65 early types Debris features: shells, ripples, and tidal tails Method: two-dimensional decoposition Result: 11/65, 3-10% of total 3.6𝜇𝑚 galaxy luminosity Same area in KR(Kormendy relation) and FP(the fundamental plane)

ETG with debris tidal debris: recent gravitational interaction or merger these galaxies have either undergone minor merging events so that the overall structural properties of the galaxies are not significantly altered, they have undergone a major merging events but already have experienced sufficient relaxation and phase mixing so that their structural properties become similar to those of the non-interacting early-type galaxies.