分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The Subaru Hyper Suprime-Cam (HSC) Strategic Survey is the latest-generation
multi-band optical imaging survey for galaxy evolution and structure formation.
The "Ultra-Deep" component of the HSC survey provides $grizy$ broad-band images
over $\sim3.4$ deg$^2$ to detection limits of $\sim26$-28 AB, along with
narrow-band images, in the COSMOS and the SXDS fields. These images provide an
unprecedented combination of depths and area coverage, for the studies galaxies
up to $z\sim7$. However, the lack of coverage at $<4000$ Ang implies incomplete
sampling of the rest-frame UV at $z\lesssim 3$, which is critically needed for
understanding the buildup of stellar mass in the later cosmic time. We
conducted a multi-year CFHT $u^\ast$-band imaging campaign in the two HSC
Ultra-Deep fields with CFHT MegaCam. By including shallower archival data, we
reach 5-$\sigma$ depths of $u^\ast=28.1$ and 28.4 (AB) at the centers of the
COSMOS and SXDS fields, respectively, and $u^\ast=27.7$ and 27.8 in the central
1 deg$^2$ fields. The image quality is $\gtrsim0.90$ arcsec, fairly good for
the $u^\ast$ band. Both the photometric and astrometric quality of our data are
excellent. We show that the combination of our $u^\ast$-band and HSC data can
lead to high-quality photometric redshifts at $z=0$-3, and robust measurements
of rest-frame UV on galaxies at $0.4
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We utilize the Hyper Suprime-Cam (HSC) Wide Survey to explore the properties of galaxies located in the voids identified from the Baryon Oscillation Spectroscopic Survey (BOSS) up to z~0.7. The HSC reaches i~25, allowing us to characterize the void galaxies down to 10$^{9.2}$ solar mass. We find that the revised void galaxy densities, when including faint galaxies in voids defined by bright galaxies, are still underdense compared to the mean density from the entire field. In addition, we classify galaxies into star-forming, quiescent, and green valley populations, and find that void galaxies tend to have slightly higher fractions of star-forming galaxies under the mass and redshift control, although the significance of this result is only moderate (2$\sigma$). However, when we focus on the star-forming population, the distribution of the specific star formation rate (sSFR) of void galaxies shows little difference from that of the control galaxies. Similarly, the median sSFR of star-forming void galaxies is also in good agreement with that of the star-forming control galaxies. Moreover, the effective green valley fraction of void galaxies, defined as the number of green valley galaxies over the number of nonquiescent galaxies, is comparable to that of the control ones, supporting the suggestion that void and control galaxies evolve under similar physical processes and quenching frequencies. Our results thus favor a scenario of the galaxy assembly bias.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present a statistical study of 180 dust continuum sources identified in 33 massive cluster fields by the ALMA Lensing Cluster Survey (ALCS) over a total of 133 arcmin$^{2}$ area, homogeneously observed at 1.2 mm. ALCS enables us to detect extremely faint mm sources by lensing magnification, including near-infrared (NIR) dark objects showing no counterparts in existing {\it Hubble Space Telescope} and {\it Spitzer} images. The dust continuum sources belong to a blind sample ($N=141$) with S/N $\gtrsim$ 5.0 (a purity of $>$ 0.99) or a secondary sample ($N=39$) with S/N= $4.0-5.0$ screened by priors. With the blind sample, we securely derive 1.2-mm number counts down to $\sim7$ $\mu$Jy, and find that the total integrated 1.2mm flux is 20.7$^{+8.5}_{-6.5}$ Jy deg$^{-2}$, resolving $\simeq$ 80 % of the cosmic infrared background light. The resolved fraction varies by a factor of $0.6-1.1$ due to the completeness correction depending on the spatial size of the mm emission. We also derive infrared (IR) luminosity functions (LFs) at $z=0.6-7.5$ with the $1/V_{\rm max}$ method, finding the redshift evolution of IR LFs characterized by positive luminosity and negative density evolution. The total (=UV+IR) cosmic star-formation rate density (SFRD) at $z>4$ is estimated to be $161^{+25}_{-21}$ % of the established measurements, which were almost exclusively based on optical$-$NIR surveys. Although our general understanding of the cosmic SFRD is unlikely to change beyond a factor of 2, these results add to the weight of evidence for an additional ($\approx 60$ %) SFRD component contributed by the faint-mm population, including NIR dark objects.