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Register a new userCosmic star formation history revealed by the AKARI, & Spatially-resolved spectroscopy of an E+A (Post-starburst) system
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We reveal cosmic star-formation history obscured by dust using deep infrared observation with the AKARI. A continuous filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24um) by the AKARI satellite allows us to estimate restframe 8um and 12um luminosities without using a large extrapolation based on a SED fit, which was the largest uncertainty in previous work. We found that restframe 8um (0.38<z<2.2), 12um (0.15<z<1.16), and total infrared (TIR) luminosity functions (LFs) (0.2<z<1.6) constructed from the AKARI NEP deep data, show a continuous and strong evolution toward higher redshift. In terms of cosmic infrared luminosity density (Omega_IR), which was obtained by integrating analytic fits to the LFs, we found a good agreement with previous work at z<1.2, with Omega_IR propto (1+z)^4.4+-1.0. When we separate contributions to Omega_IR by LIRGs and ULIRGs, we found more IR luminous sources are increasingly more important at higher redshift. We found that the ULIRG (LIRG) contribution increases by a factor of 10 (1.8) from z=0.35 to z=1.4.
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Understanding infrared (IR) luminosity is fundamental to understanding the cosmic star formation history and AGN evolution. Japanese infrared satellite, AKARI, provided unique data sets to probe this both at low and high redshift; the AKARI all sky survey in 6 bands (9-160 $mu$m), and the AKARI NEP survey in 9 bands (2-24$mu$m). The AKARI performed all sky survey in 6 IR bands (9, 18, 65, 90, 140, and 160 $mu$m) with 3-10 times better sensitivity than IRAS, covering the crucial far-IR wavelengths across the peak of the dust emission. Combined with a better spatial resolution, we measure the total infrared luminosity ($L_{TIR}$) of individual galaxies, and thus, the total infrared luminosity density of the local Universe much more precisely than previous work. In the AKARI NEP wide field, AKARI has obtained deep images in the mid-infrared (IR), covering 5.4 deg$^2$. However, our previous work was limited to the central area of 0.25 deg$^2$ due to the lack of deep optical coverage. To rectify the situation, we used the newly advent Subaru telescopes Hyper Suprime-Cam to obtain deep optical images over the entire 5.4 deg$^2$ of the AKARI NEP wide field. With this deep and wide optical data, we, for the first time, can use the entire AKARI NEP wide data to construct restframe 8$mu$m, 12$mu$m, and total infrared (TIR) luminosity functions (LFs) at 0.15$<z<$2.2. A continuous 9-band filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24$mu$m) by the AKARI satellite allowed us to estimate restframe 8$mu$m and 12$mu$m luminosities without using a large extrapolation based on a SED fit, which was the largest uncertainty in previous work. By combining these two results, we reveal dust-hidden cosmic star formation history and AGN evolution from z=0 to z=2.2, all probed by the AKARI satellite.
We have performed a spatially-resolved medium resolution long-slit spectroscopy of a nearby E+A (post-starburst) galaxy system, SDSSJ161330.18+510335.5. This E+A galaxy has an obvious companion galaxy 14kpc in front with the velocity difference of 61.8 km/s. Both galaxies have obviously disturbed morphology We have found that H$delta$ equivalent width (EW) of the E+A galaxy is greater than 7AA galaxy wide (8.5 kpc). The E+A galaxy have a weak [OIII] emission (EW$sim$1AA) by $sim$2.6 kpc offset from the peak of the Balmer absorption lines. We detected a rotational velocity in the companion galaxy of $>$175km/s. The progenitor of the companion may have been a rotationally-supported, but yet passive S0 galaxy. The age of the E+A galaxy after quenching the star formation is estimated to be 100-500 Myr, with its centre having slightly younger stellar population. These findings are inconsistent with a simple picture where the dynamical interaction creates infall of the gas reservoir that causes the central starburst/post-starburst. Instead, our results present an important example where the galaxy-galaxy interaction can trigger a galaxy-wide post-starburst phenomena.
The Calar Alto Legacy Integral Field Area (CALIFA) is an ongoing 3D spectroscopic survey of 600 nearby galaxies of all kinds. This pioneer survey is providing valuable clues on how galaxies form and evolve. Processed through spectral synthesis techniques, CALIFA datacubes allow us to, for the first time, spatially resolve the star formation history of galaxies spread across the color-magnitude diagram. The richness of this approach is already evident from the results obtained for the first 107 galaxies. Here we show how the different galactic spatial sub-components (bulge and disk) grow their stellar mass over time. We explore the results stacking galaxies in mass bins, finding that, except at the lowest masses, galaxies grow inside-out, and that the growth rate depends on a galaxys mass. The growth rate of inner and outer regions differ maximally at intermediate masses. We also find a good correlation between the age radial gradient and the stellar mass density, suggesting that the local density is a main driver of galaxy evolution.
We present deep Hubble Space Telescope Advanced Camera for Surveys observations of the stellar populations in two fields lying at 20 and 23 kpc from the centre of M31 along the south-west semi-major axis. These data enable the construction of colour-magnitude diagrams reaching the oldest main-sequence turn-offs (~13 Gyr) which, when combined with another field at 25 kpc from our previous work, we use to derive the first precision constraints on the spatially-resolved star formation history of the M31 disc. The star formation rates exhibit temporal as well as field-to-field variations, but are generally always within a factor of two of their time average. There is no evidence of inside-out growth over the radial range probed. We find a median age of ~7.5 Gyr, indicating that roughly half of the stellar mass in the M31 outer disc was formed before z ~ 1. We also find that the age-metallicity relations (AMRs) are smoothly increasing from [Fe/H]~-0.4 to solar metallicity between 10 and 3 Gyr ago, contrary to the flat AMR of the Milky Way disc at a similar number of scale lengths. Our findings provide insight on the roles of stellar feedback and radial migration in the formation and evolution of large disc galaxies.
The recent star formation histories (SFHs) of post-starburst galaxies have been determined almost exclusively from detailed modeling of their composite star light. This has provided important but limited information on the number, strength, and duration of bursts of star formation. In this work, we present a direct and independent measure of the recent SFH of S12 (plate-mjd-fiber for SDSS 623-52051-207; designated EAS12 in Smercina et al. 2018) from its star cluster population. We detect clusters from high resolution, $UBR$ optical observations from HST, and compare their luminosities and colors with stellar population models to estimate the ages and masses of the clusters. No clusters younger than $sim$70 Myr are found, indicating star formation shut off at this time. Clusters formed $sim$120 Myr ago reach masses up to $sim mbox{few}times10^7~M_{odot}$, several times higher than similar age counterparts formed in actively merging galaxies like the Antennae and NGC 3256. We develop a new calibration based on known properties for 8 nearby galaxies to estimate the star formation rate (SFR) of a galaxy from the mass of the most massive cluster, $M_{rm max}$. The cluster population indicates that S12 experienced an extremely intense but short-lived burst $sim$120 Myr ago, with an estimated peak of $500^{+500}_{-250}~M_{odot}~mbox{yr}^{-1}$ and duration of $50pm25$ Myr, one of the highest SFRs estimated for any galaxy in the nearby universe. Prior to the recent, intense burst, S12 was forming stars at a moderate rate of $sim 3{-}5~M_{odot}~mbox{yr}^{-1}$, typical of spiral galaxies. However, the system also experienced an earlier burst approximately $1{-}3$ Gyr ago. While fairly uncertain, we estimate that the SFR during this earlier burst was $sim20{-}30~M_{odot}~mbox{yr}^{-1}$, similar to the current SFR in the Antennae and NGC 3256.
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