A star formation study of the ATLAS^3Dearly-type galaxies with the AKARI all-sky survey

Abstract

Context. The star formation properties of early-type galaxies (ETGs) are currently the subject of considerable interest, particularly whether they differ from those of gas-rich spirals. Aims. We perform a systematic study of star formation in a large sample of local ETGs using polycyclic aromatic hydrocarbon (PAH) and dust emission, focusing on the galaxies' star formation rates (SFRs) and star formation efficiencies (SFEs). Methods. Our sample is composed of the 260 ETGs from the ATLAS 3D survey, from which we use the cold gas measurements (H i and CO). The SFRs are estimated from stellar, PAH and dust fits to spectral energy distributions created from new AKARI measurements and literature data from WISE and 2MASS. Results. The mid-infrared luminosities of non-CO-detected galaxies are well correlated with their stellar luminosities, showing that they trace (circum)stellar dust emission. CO-detected galaxies show an excess above these correlations, uncorrelated with their stellar luminosities, indicating that they likely contain PAHs and dust of interstellar origin. PAH and dust luminosities of CO-detected galaxies show tight correlations with their molecular gas masses, and the derived current SFRs are typically 0.01 -1 M ⊙ yr −1 . These SFRs systematically decrease with stellar age at fixed stellar mass, while they correlate nearly linearly with stellar mass at fixed age. The majority of local ETGs follow the same star-formation law as local star-forming galaxies, and their current SFEs do not depend on either stellar mass or age. Conclusions. Our results clearly indicate that molecular gas is fueling current star formation in local ETGs, that appear to acquire this gas via mechanisms regulated primarily by stellar mass. The current SFEs of local ETGs are similar to those of local star-forming galaxies, indicating that their low SFRs are likely due to smaller cold gas fractions rather than a suppression of star formation.

The Physical Properties of S0 Galaxy PGC 26218: The Origin of Starburst and Star Formation

“…of PGC 26218. Kokusho et al (2017) studied the star formation of the same sample as Davis et al (2014) in ATLAS 3D survey. They found that the local ETGs have the similar star formation efficiency to the star-forming galaxies and follow the K-S law.…”

“…The difference between them might be attributed to the methods of calculating SFR. Davis et al (2014) calculated the SFR via FUV and 22 µm, while Kokusho et al (2017) via the spectral energy distributions fitting. Colombo et al (2018) combined the CO observations made by the Combined Array for Millimeter-wave Astronomy from Extragalactic Database for Galaxy Evolution survey (Bolatto et al 2017) with the 2D-spectroscopic observations made by CAHA from Calar Alto Legacy Integral Field Area survey (Sánchez et al 2012).…”

Dust properties in the cold and hot gas phases of the ATLAS3D early-type galaxies as revealed by AKARI

“…Using the AKARI all-sky maps (Murakami et al 2007;Doi et al 2015;Ishihara et al, in prep. ), Kokusho et al (2017) systematically measured the 9, 18, 65, 90, and 140 µm band fluxes of the ATLAS 3D ETGs. They performed aperture photometry within a circular aperture of radius R aper = (2R e ) 2 + (1.5D PSF ) 2 , where R e and D PSF are respectively the effective radius of the galaxy in the optical B band (Cappellari et al 2011a) and the full width at half maximum of the AKARI point spread function (PSF) in the relevant band (Ishihara et al 2010;Takita et al 2015).…”

“…They performed aperture photometry within a circular aperture of radius R aper = (2R e ) 2 + (1.5D PSF ) 2 , where R e and D PSF are respectively the effective radius of the galaxy in the optical B band (Cappellari et al 2011a) and the full width at half maximum of the AKARI point spread function (PSF) in the relevant band (Ishihara et al 2010;Takita et al 2015). Combining the AKARI measurements with Wide-field Infrared Survey Explorer (WISE; Cutri et al 2013) and Two Micron All Sky Survey (2MASS; Skrutskie et al 2006;Griffith et al 2015) data, Kokusho et al (2017) decomposed the resulting spectral energy distributions (SEDs) into polycyclic aromatic hydrocarbon (PAH), warm dust, and cold dust emission. For the dust emission, Kokusho et al (2017) used a two-temperature modified blackbody model with fixed emissivity power-law index β = 2.…”

“…They used a circular aperture of radius R aper = 2R e , identical to our infrared photometry apertures except for our inclusion of the AKARI PSF extents. Kokusho et al (2017) detected FIR dust emission in 45% of the ATLAS 3D galaxies, where a FIR detection is defined as a robust detection in at least one of the three AKARI FIR bands. The FIR detection rate is 27% and 52% for the ATLAS 3D elliptical and lenticular galaxies, respectively, showing that lenticulars are more likely to contain cold dust.…”