MOIRCS is a fully cryogenic near-infrared instrument for the 8.2 m Subaru Telescope. MOIRCS has two observation modes: a wide-field imaging mode and a multiobject spectroscopy mode. This paper ...describes the imaging mode, its specifications, and actual performances that we confirmed through laboratory tests and commissioning observations. The imaging mode provides a 4'
$\times$
7' field of view with a pixel scale of 0”.117pixel
$^{-1}$
in the wavelength range of 0.85 to 2.5
$\mu$
using cooled optics and two 2048
$\times$
2048 HgCdTe HAWAII-2 focal plane arrays. Good-quality images are obtained over the entire field of view with practically no chromatic aberration. The limiting magnitudes for a point source estimated from observed background brightness and throughput are 23.7 in the
$J$
band, 23.0 in the
$H$
band, and 22.6 in the
$K_{\rm s}$
band (Vega) with
$S/N$
$=$
5, 0”.5 seeing, 1”.0 aperture, and 1hr exposure.
We present deep
$J$
-,
$H$
-, and
$K_{\rm s}$
-band imaging data of the MOIRCS Deep Survey (MODS), which was carried out with the Multi-Object Infrared Camera and Spectrograph (MOIRCS) mounted on the ...Subaru Telescope in the GOODS-North region. The data reach 5
$\ \sigma$
total limiting magnitudes for point sources of
$J$
$=$
23.9,
$H$
$=$
22.8, and
$K_{\rm s}$
$=$
22.8 (Vega magnitude) over 103 arcmin
$^{2}$
(wide field). In 28 arcmin
$^{2}$
of the survey area, which is an ultra-deep field of the MODS (deep field), the data reach 5
$\ \sigma$
depths of
$J$
$=$
24.8,
$H$
$=$
23.4, and
$K_{\rm s}$
$=$
23.8. The spatial resolutions of the combined images are FWHM
$\sim\ $
0
$''\!\!\!.$
6 and
$\sim\ $
0
$''\!\!\!.$
5 for the wide and deep fields in all bands, respectively. Combining the MODS data with the multi-wavelength public data taken with the HST, Spitzer, and other ground-based telescopes in the GOODS field, we constructed a multi-wavelength photometric catalog of
$K_{\rm s}$
-selected sources. Using the catalog, we present
$K_{\rm s}$
-band number counts and near-infrared color distribution of the detected objects; we also demonstrate some selection techniques with the NIR colors for high redshift galaxies. These data and catalog are publicly available via Internet.
MOIRCS Deep Survey. I: DRG Number Counts Kajisawa, Masaru; Konishi, Masahiro; Suzuki, Ryuji ...
Publications of the Astronomical Society of Japan,
12/2006, Volume:
58, Issue:
6
Journal Article
Peer reviewed
Open access
We used very deep near-infrared imaging data taken with the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) on the Subaru Telescope to investigate the number counts of Distant Red Galaxies ...(DRGs). We observed a
$4' \times 7'$
field in the Great Observatories Origins Deep Survey-North (GOODS-N), and our data reached
$J=24.6$
and
$K=23.2$
(
$5\,\sigma$
, Vega magnitude). The surface density of DRGs selected by
$J-K \gt 2.3 J-K \gt 2.3$
is
$2.35 \pm 0.31 \,\mathrm{arcmin}^{-2}$
at
$K < 22$
and
$3.54 \pm 0.38 \,\mathrm{arcmin}^{-2}$
at
$K < 23$
, respectively. These values are consistent with those in the GOODS-South and FIRES. Our deep and wide data suggest that the number counts of DRGs turn over at
$K \sim 22$
, and the surface density of the faint DRGs with
$K \gt 22$
is smaller than that expected from the number counts at the brighter magnitude. The result indicates that while there are many bright galaxies at
$2 < z < 4$
with the relatively old stellar population and/or heavy dust extinction, the number of faint galaxies with a similar red color is relatively small. Different behavior patterns of the number counts of the DRGs and bluer galaxies with
$2 < z_{\mathrm{phot}} < 4$
at
$K \gt 22$
suggest that the mass-dependent color distribution, where most of the low-mass galaxies are blue, while more massive galaxies tend to have redder colors, had already been established at that epoch.
We present the first measurement of clustering properties of low-mass galaxies with a stellar mass down to
$M_*\sim 10^9 M_{\odot}$
at 1
$\lt z \lt $
4 in 24.4 arcmin
$^{2}$
of the GOODS-North region ...with a depth of
$K_\mathrm{AB}\sim$
25. Luminous galaxies in the
$K$
-band have a larger correlation length than faint galaxies. For color-selected samples at 2
$\lt z \lt$
4, distant red galaxies with
$J-K \gt$
1.3 show a large bias of
$b\sim$
7.2
$\pm$
1.3 on scales of up to
$\theta\sim$
100
$^{\prime\prime}$
or 3.1 comoving Mpc, while blue galaxies with 0.5
$\lt J-K \lt $
1.3 have a weak clustering signal on large scales, but a possible strong small-scale excess at
$\theta \lt $
10
$^{\prime\prime}$
. For massive galaxies with
$M_*\gtrsim 10^{10}M_{\odot}$
, we estimate the correlation length and bias to be
$r_0\sim$
4.5
$h^{-1}$
Mpc and
$b=$
1.9–3.5, which are much larger than those of low-mass (
$M_*\sim$
10
$^9-10^{10}M_{\odot}$
) galaxies. The comparison of our measurements with analytic CDM models constrains the properties of hosting dark halos, and indicates that the low-mass galaxies would be progenitors of galaxies with a typical luminosity of
$L\lesssim L_*$
in the local Universe. The blue galaxies in low-mass samples are more strongly clustered in more massive halos with higher occupation numbers than low-mass red galaxies. This fact suggests an environment effect due to the halo mass on the star-formation activity at high-
$z$
.
We present the results of deep near-infrared imaging observations of the
$z=3.1$
proto-cluster region in the SSA 22a field taken by MOIRCS mounted on the Subaru Telescope. We observed a 21.7 arcmin
...$^2$
field to depths of
$J=$
24.5,
$H=$
24.3, and
$K=$
23.9 (5
$\sigma$
). We examined the distribution of the
$K$
-selected galaxies at
$z \sim 3$
by using a simple color cut for distant red galaxies (DRGs) as well as a photometric-redshift selection technique. The marginal density excess of DRGs and the photo-
$z$
selected objects were found around the two most luminous Ly
$\alpha$
blobs (LABs). We investigated the correlation between the
$K$
-selected objects and the LABs, and found that several galaxies with stellar mass,
$M_* = 10^{9}$
–
$10^{11} M_\odot$
, exist in the vicinity of LABs, especially around the two most luminous ones. We also found that 7 of the 8LABs in the field have plausible
$K_{\rm s}$
-band counterparts, and the sum of the stellar mass possibly associated with LABs correlates with their luminosity and surface brightness, which implies that the origin of Ly
$\alpha$
emission may be closely correlated with their previous star-formation phenomena.
We investigated rest-frame near-infrared (NIR) morphologies of a sample of 139 galaxies with
$M_{\mathrm{s}}$
$\geq$
1
$\times$
10
$^{10}\ M_{\odot}$
at z
$=$
0.8–1.2 in the GOODS-North field using ...our deep NIR imaging data (MOIRCS Deep Survey, MODS). We focused on Luminous Infrared Galaxies (LIRGs), which dominate a high star formation rate (SFR) density at z
$\sim $
1, in a sample identified by cross-correlating with the Spitzer/MIPS 24
$\mu $
m source catalog. We performed two-dimensional light profile fimonospaceings of z
$\sim $
1 galaxies in the
$K_{\mathrm{s}}$
-band (rest-frame
$J$
-band) with a single-component Sérsic model. We found that at z
$\sim $
1,
$\sim $
90% of the LIRGs have low Sérsic indices (
$n$
$\lt$
2.5, similar to disk-like galaxies) in the
$K_{\mathrm{s}}$
-band, and that those disk-like LIRGs consist of
$\sim $
60% of the whole disk-like sample above
$M_{\mathrm{s}}$
$\geq$
3
$\times$
10
$^{10}\ M_{\odot}$
. The z
$\sim $
1 disk-like LIRGs are comparable to or
$\sim $
20% scer at the maximum in size compared to local disk-like galaxies in the same stellar mass range. When we examined rest-frame UV–optical morphologies using the HST/ACS images, the rest-frame
$B$
-band sizes of the z
$\sim $
1 disk-like galaxies were found to be comparable to those of the local disk-like galaxies, as reported by previous studies on the size evolution of disk-like galaxies in the rest-frame optical band. By measuring color gradients (galaxy sizes as a function of wavelength) of the z
$\sim $
1 and local disk-like galaxies, we found that the z
$\sim $
1 disk-like galaxies have a 3–5 times steeper color gradient than the local ones. Our results indicate that (i) more than a half of the relatively massive disk-like galaxies at z
$\sim $
1 are in violent star-formation epochs observed as LIRGs, and also (ii) that most of those LIRGs are constructing their fundamental disk structure vigorously. The high SFR density in the universe at z
$\sim $
1 may be dominated by such star formation in the disk region in massive galaxies.
The effect of oxide coating on the activity of a copper-zinc oxide-based catalyst for methanol synthesis via the hydrogenation of carbon dioxide was investigated. A commercial catalyst was coated ...with various oxides by a sol-gel method. The influence of the types of promoters used in the sol-gel reaction was investigated. Temperature-programmed reduction-thermogravimetric analysis revealed that the reduction peak assigned to the copper species in the oxide-coated catalysts prepared using ammonia shifts to lower temperatures than that of the pristine catalyst; in contrast, the reduction peak shifts to higher temperatures for the catalysts prepared using L(+)-arginine. These observations indicated that the copper species were weakly bonded with the oxide and were easily reduced by using ammonia. The catalysts prepared using ammonia show higher CO₂ conversion than the catalysts prepared using L(+)-arginine. Among the catalysts prepared using ammonia, the silica-coated catalyst displayed a high activity at high temperatures, while the zirconia-coated catalyst and titania-coated catalyst had high activity at low temperatures. At high temperature the conversion over the silica-coated catalyst does not significantly change with reaction temperature, while the conversion over the zirconia-coated catalyst and titania-coated catalyst decreases with reaction time. From the results of FTIR, the durability depends on hydrophilicity of the oxides.
We present the results of near-infrared multi-object spectroscopic observations for 37 BzK-color-selected star-forming galaxies conducted with MOIRCS on the Subaru Telescope. The sample is drawn from ...the K{sub s} -band-selected catalog of the MOIRCS Deep Survey in the GOODS-N region. About half of our samples are selected from the publicly available 24 {mu}m-source catalog of the Multiband Imaging Photometer for Spitzer on board the Spitzer Space Telescope. H{alpha} emission lines are detected from 23 galaxies, of which the median redshift is 2.12. We derived the star formation rates (SFRs) from extinction-corrected H{alpha} luminosities. The extinction correction is estimated from the spectral energy distribution (SED) fitting of multiband photometric data covering UV to near-infrared wavelengths. The Balmer decrement of the stacked emission lines shows that the amount of extinction for the ionized gas is larger than that for the stellar continuum. From a comparison of the extinction-corrected H{alpha} luminosity and other SFR indicators, we found that the relation between the dust properties of stellar continuum and ionized gas is different depending on the intrinsic SFR (differential extinction). We compared SFRs estimated from extinction-corrected H{alpha} luminosities with stellar masses estimated from SED fitting. The comparison shows no correlation between SFR and stellar mass. Some galaxies with stellar mass smaller than {approx}10{sup 10} M{sub sun} show SFRs higher than {approx}100 M{sub sun} yr{sup -1}. The specific SFRs (SSFRs) of these galaxies are remarkably high; galaxies which have SSFR higher than {approx}10{sup -8} yr{sup -1} are found in eight of the present sample. From the best-fit parameters of SED fitting for these high-SSFR galaxies, we find that the average age of the stellar population is younger than 100 Myr, which is consistent with the implied high SSFR. The large SFR implies the possibility that the high-SSFR galaxies significantly contribute to the cosmic SFR density of the universe at z {approx} 2. When we apply the larger extinction correction for the ionized gas or the differential extinction correction, the total SFR density estimated from the H{alpha}-emission-line galaxies is 0.089-0.136 M{sub sun} yr{sup -1} Mpc{sup -3}, which is consistent with the total SFR densities in the literature. The metallicity of the high-SSFR galaxies, which is estimated from the N2 index, is larger than that expected from the mass-metallicity relation of UV-selected galaxies at z {approx} 2 by Erb et al.
We present the results of wide-field deep JHK imaging of the SSA22 held using the MOIRCS instrument equipped with the Subaru telescope. The observed field is 112 arcmin super(2) in area, which covers ...the z = 3.1 protocluster characterized by the overdensities of Ly alpha emitters (LAEs) and Ly alpha blobs (LABs). The 5sigma limiting magnitude is K sub(AB) = 24.3. We extract the potential protocluster members from the K-selected sample by using the multi-band photometric-redshift selection as well as the simple color cut for distant red galaxies (DRGs; J - K sub(AB) > 1.4). The surface number density of DRGs in our observed fields shows clear excess compared with those in the blank fields, and the location of the densest area whose projected overdensity is twice the average coincides with the large-scale density peak of LAEs. We also found that K-band counterparts with z sub(phot) Asymptotically = to 3.1 are detected for 75% (15/20) of the LABs within their Ly alpha halo, and the 40% (8/20) of LABs have multiple components, which gives a direct evidence of the hierarchical multiple merging in galaxy formation. The stellar mass of LABs correlates with their luminosity, isophotal area, and the Ly alpha velocity widths, implying that the physical scale and the dynamical motion of Ly alpha emission are closely related to their previous star formation activities. Highly dust-obscured galaxies such as hyper extremely red objects (J - K sub(AB) > 2.1) and plausible K-band counterparts of submillimeter sources are also populated in the high-density region.
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