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Register a new userStar Formation at $4 < z < 6$ From the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH)
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Using the first 50% of data collected for the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) observations on the 1.8 deg$^2$ Cosmological Evolution Survey (COSMOS) we estimate the masses and star formation rates of 3398 $M_*>10^{10}M_odot $ star-forming galaxies at $4 < z < 6$ with a substantial population up to $M_* gtrsim 10^{11.5} M_odot$. We find that the strong correlation between stellar mass and star formation rate seen at lower redshift (the main sequence of star-forming galaxies) extends to $zsim6$. The observed relation and scatter is consistent with a continued increase in star formation rate at fixed mass in line with extrapolations from lower-redshift observations. It is difficult to explain this continued correlation, especially for the most massive systems, unless the most massive galaxies are forming stars near their Eddington-limited rate from their first collapse. Furthermore, we find no evidence for moderate quenching at higher masses, indicating quenching either has not occurred prior to $z sim 6$ or else occurs rapidly, so that few galaxies are visible in transition between star-forming and quenched.
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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 present a catalog of extended low-surface-brightness galaxies (LSBGs) identified in the Wide layer of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first ${sim}$200 deg$^2$ of the survey, we have uncovered 781 LSBGs, spanning red ($g-igeq0.64$) and blue ($g-i<0.64$) colors and a wide range of morphologies. Since we focus on extended galaxies ($r_mathrm{eff}=2.5$-$14^{primeprime}$), our sample is likely dominated by low-redshift objects. We define LSBGs to have mean surface brightnesses $bar{mu}_mathrm{eff}(g)>24.3$ mag arcsec$^{-2}$, which allows nucleated galaxies into our sample. As a result, the central surface brightness distribution spans a wide range of $mu_0(g)=18$-$27.4$ mag arcsec$^{-2}$, with 50% and 95% of galaxies fainter than 24.3 and 22 mag arcsec$^{-2}$, respectively. Furthermore, the surface brightness distribution is a strong function of color, with the red distribution being much broader and generally fainter than that of the blue LSBGs, and this trend shows a clear correlation with galaxy morphology. Red LSBGs typically have smooth light profiles that are well-characterized by single-component S{e}rsic functions. In contrast, blue LSBGs tend to have irregular morphologies and show evidence for ongoing star formation. We crossmatch our sample with existing optical, HI, and ultraviolet catalogs to gain insight into the physical nature of the LSBGs. We find that our sample is diverse, ranging from dwarf spheroidals and ultra-diffuse galaxies in nearby groups to gas-rich irregulars to giant LSB spirals, demonstrating the potential of the HSC-SSP to provide a truly unprecedented view of the LSBG population.
We present the quasar luminosity function at $z sim 5$ derived from the optical wide-field survey data obtained as a part of the Subaru strategic program (SSP) with Hyper Suprime-Cam (HSC). From $sim$81.8 deg$^2$ area in the Wide layer of the HSC-SSP survey, we selected 224 candidates of low-luminosity quasars at $z sim 5$ by adopting the Lyman-break method down to $i = 24.1$ mag. Based on our candidates and spectroscopically-confirmed quasars from the Sloan Digital Sky Survey (SDSS), we derived the quasar luminosity function at $z sim 5$ covering a wide luminosity range of $-28.76 < M_{rm 1450} < -22.32$ mag. We found that the quasar luminosity function is fitted by a double power-law model with a break magnitude of $M^{*}_{1450} = -25.05^{+0.10}_{-0.24}$ mag. The inferred number density of low-luminosity quasars is lower, and the derived faint-end slope, $-1.22^{+0.03}_{-0.10}$, is flatter than those of previous studies at $z sim 5$. A compilation of the quasar luminosity function at $4 leq z leq 6$ from the HSC-SSP suggests that there is little redshift evolution in the break magnitude and in the faint-end slope within this redshift range, although previous studies suggest that the faint-end slope becomes steeper at higher redshifts. The number density of low-luminosity quasars decreases more rapidly from $z sim 5$ to $z sim 6$ than from $z sim 4$ to $z sim 5$.
We present an overview of a deep transient survey of the COSMOS field with the Subaru Hyper Suprime-Cam (HSC). The survey was performed for the 1.77 deg$^2$ ultra-deep layer and 5.78 deg$^2$ deep layer in the Subaru Strategic Program over 6- and 4-month periods from 2016 to 2017, respectively. The ultra-deep layer shows a median depth per epoch of 26.4, 26.3, 26.0, 25.6, and 24.6 mag in $g$, $r$, $i$, $z$, and $y$ bands, respectively; the deep layer is $sim0.6$ mag shallower. In total, 1,824 supernova candidates were identified. Based on light curve fitting and derived light curve shape parameter, we classified 433 objects as Type Ia supernovae (SNe); among these candidates, 129 objects have spectroscopic or COSMOS2015 photometric redshifts and 58 objects are located at $z > 1$. Our unique dataset doubles the number of Type Ia SNe at $z > 1$ and enables various time-domain analyses of Type II SNe, high redshift superluminous SNe, variable stars, and active galactic nuclei.
We present the first results of the Subaru/Hyper Suprime-Cam (HSC) survey of the interacting galaxy system, NGC4631 and NGC4656. From the maps of resolved stellar populations, we identify 11 dwarf galaxies (including already-known dwarfs) in the outer region of NGC4631 and the two tidal stellar streams around NGC4631, named Stream SE and Stream NW, respectively. This paper describes the fundamental properties of these tidal streams. Based on the tip of red giant branch method and the Bayesian statistics, we find that StreamSE (7.10 Mpc in Expected a posteriori, EAP, with the 90% credible intervals of [6.22, 7.29] Mpc) and StreamNW (7.91 Mpc in EAP with the 90% credible intervals of [6.44, 7.97] Mpc) are located in front of and behind NGC4631, respectively. We also calculate the metallicity distribution of stellar streams by comparing the member stars with theoretical isochrones on the color-magnitude diagram. We find that both streams have the same stellar population based on the Bayesian model selection method, suggesting that they originated from a tidal interaction between NGC4631 and a single dwarf satellite. The expected progenitor has a positively skewed metallicity distribution function with [M/H]_EAP=-0.92 with the 90% credible intervals of [-1.46, -0.51]. The stellar mass of the progenitor is estimated as 3.7 x 10e+8 Msun with the 90% credible intervals of [5.8 x 10e+6, 8.6 x 10e+9] Msun based on the mass-metallicity relation for Local group dwarf galaxies. This is in good agreement with an initial stellar mass of the progenitor presumed in the previous N-body simulation.
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