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.
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 examine whether the spectral energy distribution of optical continuum emission of active galactic nuclei (AGNs) changes during flux variation, based on accurate and frequent monitoring ...observations of 11 nearby Seyfert galaxies and QSOs carried out in the B, V, and I bands for seven years by the MAGNUM telescope. The multi-epoch flux data in any two different bands obtained on the same night show a very tight linear flux-to-flux relationship for all target AGNs. The flux of the host galaxy within the photometric aperture is carefully estimated by surface brightness fitting to available high-resolution Hubble Space Telescope images and MAGNUM images. The flux of narrow emission lines in the photometric bands is also estimated from available spectroscopic data. We find that the non-variable component of the host galaxy plus narrow emission lines for all target AGNs is located on the fainter extension of the linear regression line of multi-epoch flux data in the flux-to-flux diagram. This result strongly indicates that the spectral shape of AGN continuum emission in the optical region ({approx}4400-7900 A) does not systematically change during flux variation. The trend of spectral hardening that optical continuum emission becomes bluer as it becomes brighter, which has been reported by many studies, is therefore interpreted as the domination of the variable component of the nearly constant spectral shape of an AGN as it brightens over the non-variable component of the host galaxy plus narrow lines, which is usually redder than AGN continuum emission.
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.
We present spectroscopy of 15 star-forming BzK galaxies (sBzKs) with K AB 23 in the Subaru Deep Field, for which H alpha and some other emission lines are detected in 0.9-2.3 is a subset of spectra ...with a resolution of R = 500. Using H alpha luminosities, we obtain star formation rates (SFRs), and then specific SFRs (SSFRs) dividing SFRs by stellar masses, which are derived from SED fitting to BVRi'z'K photometry. It is found that sBzKs with higher stellar masses have larger SFRs. A negative correlation is seen between stellar mass and SSFR, which is consistent with the previous results for z ~ 2 galaxies. This implies that a larger growth of stellar mass occurs in less massive galaxies. In addition, gas-phase oxygen abundances, 12+log(O/H), are derived from the ratio of N II( lambda 6584) to H alpha using the N2 index method. We have found a correlation between stellar mass and oxygen abundance in the sense that more massive sBzKs tend to be more metal rich, which is qualitatively consistent with the relation for UV-selected z ~ 2 galaxies. However, the metallicity of the sBzKs is ~0.2 dex higher than that of UV-selected galaxies with similar stellar masses, which is significant considering the small uncertainties. The sBzKs in our sample have redder R - K colors than the UV-selected galaxies. This galaxy color dependence in the oxygen abundance may be caused by older or dustier galaxies having higher metallicities at z ~ 2.
We have developed high-dispersion VPH (volume phase holographic) grisms with zinc selenide (ZnSe) prisms for the cryogenic optical system of MOIRCS (Multi-Object near-InfraRed Camera and ...Spectrograph) for Y-, J-, H-, and K-band observations. We fabricated VPH gratings using a hologram resin. After several heat cycles at between room temperature and 120 K, the VPH gratings were assembled to grisms by gluing with two ZnSe prisms. Several heat cycles were also carried out for the grisms before being installed into MOIRCS. We measured the efficiencies of the VPH grisms in a laboratory, and found them to be 70%–82%. The performances obtained by observations of MOIRCS with the 8.2 m Subaru Telescope have been found to be very consistent with the results in the laboratory test. This is the first astronomical application of cryogenic VPH grisms.
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.
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