A systematic study of dust and star formationin early-type galaxies with AKARI

Takuma Kokusho1, Hidehiro Kaneda1, Martin Bureau2, Toyoaki Suzuki1, Mitsuyoshi Yamagishi3, Takashi Onaka4

1Nagoya University, 2University of Oxford, 3ISAS/JAXA, 4University of Tokyo

1. IntroductionEarly-type galaxies (ETGs): elliptical (E) / lenticular (S0) galaxies¾ filled with hot X-ray plasma (destructive of dust)¾ dominated by old stars (less productive of dust)¾ However recent observations detect observable amounts of dust & PAHs from many

ETGs, yet their supply channels are not well understood.We perform a systematic study of dust and star formation for a large sample of ETGs.

2. Sample & dataSample: ATLAS3D 260 ETGs (MK<-21.5, D<42 Mpc; Cappellari+11)

3. Results & Discussion

no dust? no star formation?

Dust emission

Dust & stellar masses

Dust & cold gas

4. Conclusion

Line: KS law of late-type galaxies(grey region shows its1σ scatter)

¾ Fast rotators follow the KS law of late-type galaxies⇒

54 fast rotators detected in CO

¾ AKARI all-sky surveys: 9, 18, 65, 90 & 140 µm bandsData

¾ Kinematic classification (Emsellem+11)

Fast rotator (224/260) Slow rotator (36/260)

¾ 2MASS & WISE catalog: K, 3.6, 4.2, 12 & 22 μm bands¾ Literature measurements of the cold (CO & HI) & X-ray

gas phases

New dust measurements for the ATLAS3D ETGs (Kokusho+17)

regular velocity field, ≒S0 complex velocity field, ≒E

[MJy/sr]

Raper= (2Re)2+(1.5DPSF)2

sky: 1.5Raper ―2.5Raper

Re: effective radiusDPSF: FWHM of PSF

¾ Aperture photometry

𝑀 =𝐹 𝐷

𝜅 𝐵 (𝑇 )κν=13.9 cm2/g(@140 µm; Draine 03)

Mdust expected from the balance b/w supply from old stars (Mdust=1.7×10-12 Mstar [Msun/yr]; Knapp+92, Cappellari+13) & destruction in X-ray plasma with denoted timescales

¾ No correlation b/w Mdust & Mstar¾ Some ETGs are well above the

expected Mdust⇒Dust of external origin? Star formation properties of fast rotators

Dust & diffuse X-ray plasma(X-ray point sources are removed, 42 ETGs observed with Chandra; Su+15)

¾ SED fittingstar: power lawPAH: Draine&Li 07 modelwarm & cold dust: ∝ν2B(T)

⇒Mdust (=Mwarm+Mcold), LPAH

Fast rotators form stars with efficiencies similar to late-type galaxies, suggesting that their star formation may not be suppressed

¾ Mdust vs. Mgas (global HI)

¾ Correlation b/w Mdust & central Mgas like late-type galaxies⇒dense ISM of ETGs has Mdust/Mgas similar to late-type galaxies

¾ Inclusion of outer HI weakens the correlation ⇒dust-poor diffuse HI envelope?

¾ Mdust/Mstar vs. LX/Mstar ¾ SFR vs. LX (LPAH-based SFRs for ETGs; Kokusho+17)

¾ Mdust/Mstar is correlated with LX/Mstar in fast rotators, whose SFRs are also correlated with LX⇒residual star formation may cause the dust-to-X-ray correlation

¾ Mdust/Mstar is anti-correlated with LX/Mstar in slow rotators⇒dust destruction in diffuse X-ray plasma

¾ Kennicutt-Schmidt (KS) law:ΣSFR∝(Σgas)n

(n=1.4 for late-type galaxies; Kennicutt 98)

Dust and PAH emission are detected from many ETGs, that may have acquired the cold ISM through external paths.Fast rotators show correlation between dust and X-rays, which appears to be caused by their higher current star formation activities than slow rotators.

References:Cappellari et al. 2011, MNRAS, 413, 813Cappellari et al. 2013b, MNRAS, 432, 1862

Knapp et al. 1992, ApJ, 399, 76 Kokusho et al. 2017, A&A, 605, A74Mineo et al. 2012, MNRAS, 426, 1870Serra et al. 2012, MNRAS, 422, 1835

Shipley et al. 2016, ApJ, 818, 60Su et al. 2015, ApJ, 806, 156Young et al. 2011, MNRAS, 414,940

(Mineo+12)

stellar velocity maps

Fast rotators follow the KS law of late-type galaxies, suggesting that their star formation may not be strongly suppressed.

Draine 2003, ARA&A, 41, 241Draine & Li. 2007, ApJ, 657, 810Emsellem et al. 2007, MNRAS, 379, 401Kennicutt 1998, ApJ, 498, 541

(http://chandra.harvard.edu/photo/2006/galaxies)

X-ray (Chandra) Optical

¾ Mdust vs. Mgas (central HI ~34”x45”)

FIR detection rates ( )Fast rotator: 42% Slow rotator: 46%

Relation of our Galaxy (line) & a factor 2 spread around it (gray; Draine+07)

fast rotator slow rotator

(CO & HI measurements for 260 & 166 ETGs, respectively: Young+11, Serra+12, Young+14)

Open: not observed in HI Open: not observed in HI

S/N>3 in at least one of the 65, 90 & 140 µm bands