Fiber Multi-Object Spectrograph Research Articles

Improved Measurements of Galaxy Star Formation Stochasticity from the Intrinsic Scatter of Burst Indicators

Measurements of short-timescale star formation variations (i.e., “burstiness” or star formation stochasticity) are integral to our understanding of star formation feedback mechanisms and the assembly of stellar populations in galaxies. We expand upon the work of Broussard et al. by introducing a new analysis of galaxy star formation burstiness that accounts for variations in the distribution, a major confounding factor. We use Balmer decrements from the MOSFIRE Deep Evolution Field (MOSDEF) survey to measure Q sg , which we use to construct mock catalogs from the Santa Cruz Semi-Analytic Models and Mufasa cosmological hydrodynamical simulation based on 3D-HST, Fiber Multi-Object Spectrograph (FMOS)-COSMOS, and MOSDEF galaxies with Hα detections. The results of the mock catalogs are compared against observations using the burst indicator , with the standard deviation of the η distribution indicating burstiness. We find decent agreement between mock and observed η distribution shapes; however, the FMOS-COSMOS and MOSDEF mocks show a systematically low median and scatter in η in comparison to the observations. This work also presents the novel approach of analytically deriving the relationship between the intrinsic scatter in η, scatter added by measurement uncertainties, and observed scatter, resulting in an intrinsic burstiness measurement of 0.06–0.16 dex.

The Nebular Properties of Star-forming Galaxies at Intermediate Redshift from the Large Early Galaxy Astrophysics Census

We present a detailed study of the partial rest-optical (λ obs ≈ 3600–5600 Å) spectra of N = 767 star-forming galaxies at 0.6 < z < 1.0 from the Large Early Galaxy Astrophysics Census (LEGA-C). We compare this sample with low-redshift (z ∼ 0) galaxies from the Sloan Digital Sky Survey (SDSS), intermediate-redshift (z ∼ 1.6) galaxies from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS Survey, and high-redshift (z ∼ 2) galaxies from the Keck Baryonic Structure Survey (KBSS). At a look-back time of 6–8 Gyr, galaxies with stellar masses appear remarkably similar to z ∼ 0 galaxies in terms of their nebular excitation, as measured using [O iii] λ5008/Hβ. There is some evidence that 0.6 < z < 1.0 galaxies with lower M * have higher [O iii] λ5008/Hβ than z ∼ 0 galaxies and are more similar to less evolved z ∼ 1.6 and z ∼ 2 galaxies, which are offset from the z ∼ 0 locus at all M *. We explore the impact of selection effects, contributions from active galactic nuclei, and variations in physical conditions (ionization parameter and gas-phase oxygen abundance) on the apparent distribution of [O iii] λ5008/Hβ and find somewhat higher ionization in 0.6 < z < 1.0 galaxies with lower M * relative to z ∼ 0 galaxies. We use new near-infrared spectroscopic observations of a subsample of LEGA-C galaxies to investigate other probes of enrichment and excitation. Our analysis demonstrates the importance of obtaining complete rest-optical spectra of galaxies in order to disentangle these effects.

Fitting spectral energy distributions of FMOS-COSMOS emission-line galaxies atz∼ 1.6: Star formation rates, dust attenuation, and [OIII]λ5007 emission-line luminosities

We perform a spectral energy distribution fitting analysis on a COSMOS photometric sample covering the ultra-violet up to the far-infrared wavelengths and including emission lines from the Fiber Multi-Object Spectrograph survey. The sample consists of 182 objects with Hαand [OIII]λ5007 emission line measurements lying in a redshift range of 1.40 &lt; z &lt; 1.68. We obtain robust estimates of the stellar mass and star-formation rate spanning over a range of 109.5 − 1011.5M⊙and 101 − 103M⊙yr−1from the Bayesian analysis performed with CIGALE and using continuum photometry and Hαfluxes. Combining photometry and spectroscopy gives secure estimations of the amount of dust attenuation for both continuum and line emissions. We obtain a median attenuation ofAHα = 1.16 ± 0.19 mag andA[OIII] = 1.41 ± 0.22 mag. Hαand [OIII]λ5007 attenuations are found to increase with stellar mass, confirming previous findings with Hα. A difference of 57% in the attenuation experienced by emission lines and continuum is found to be in agreement with the emission lines being more attenuated than the continuum emission. Implementation of new CLOUDY HII-region models in CIGALE enables good fits of the Hα, Hβ, [OIII]λ5007 emission lines with discrepancies smaller than 0.2 dex in the predicted fluxes. Fitting the [NII]λ6584 line is found challenging due to well-known discrepancies in the locus of galaxies in the [NII]-BPT diagram at intermediate and high redshifts. We find a positive correlation between SFR andL[OIII]λ5007 after correcting for dust attenuation and we derive the linear relation log10(SFR/M⊙yr−1)=log10(L[OIII]/ergs s−1)−(41.20 ± 0.02). Leaving the slope as a free parameter leads to log10(SFR/M⊙yr−1)=(0.83 ± 0.06)log10(L[OIII]/ergs s−1)−(34.01 ± 2.63). The spread in the relation is driven by differences in the gas-phase metallicity and ionization parameter accounting for a 0.24 dex and 1.1 dex of the dispersion, respectively. We report an average value of logU ≈ −2.85 for this sample of galaxies. Including HII-region models to fit simultaneously photometric data and emission line fluxes is paramount to analyses of upcoming data sets from large spectroscopic surveys of the future, such as MOONS and PFS.

The Mass Relations between Supermassive Black Holes and Their Host Galaxies at 1 &lt; z &lt; 2 with HST-WFC3

Abstract Correlations between the mass of a supermassive black hole (SMBH) and the properties of its host galaxy (e.g., total stellar mass M *, luminosity L host) suggest an evolutionary connection. A powerful test of a coevolution scenario is to measure the relations  BH –L host and  BH –M * at high redshift and compare with local estimates. For this purpose, we acquired Hubble Space Telescope (HST) imaging with WFC3 of 32 X-ray-selected broad-line (type 1) active galactic nuclei at 1.2 &lt; z &lt; 1.7 in deep survey fields. By applying state-of-the-art tools to decompose the HST images including available ACS data, we measured the host galaxy luminosity and stellar mass along with other properties through the two-dimensional model fitting. The black hole mass (  BH ) was determined using the broad Hα line, detected in the near-infrared with the Subaru Fiber Multi-Object Spectrograph, which potentially minimizes systematic effects using other indicators. We find that the observed ratio of  BH to total M * is 2.7× larger at z ∼ 1.5 than in the local universe, while the scatter is equivalent between the two epochs. A nonevolving mass ratio is consistent with the data at the 2σ–3σ confidence level when accounting for selection effects (estimated using two independent and complementary methods) and their uncertainties. The relationship between  BH and host galaxy total luminosity paints a similar picture. Therefore, our results cannot distinguish whether SMBHs and their total host stellar mass and luminosity proceed in lockstep or whether the growth of the former somewhat overshoots the latter, given the uncertainties. Based on a statistical estimate of the bulge-to-total mass fraction, the ratio  BH /M *,bulge is offset from the local value by a factor of ∼7, which is significant even accounting for selection effects. Taken together, these observations are consistent with a scenario in which stellar mass is subsequently transferred from an angular momentum–supported component of the galaxy to a pressure-supported one through secular processes or minor mergers at a faster rate than mass accretion onto the SMBH.

An Observational Link between AGN Eddington Ratio and [N ii]λ6583/Hα at 0.6 &lt; z &lt; 1.7

Abstract We present an observed relationship between the Eddington ratio (λ Edd) and the optical narrow-emission-line ratio ([N ii]λ6583/Hα) of X-ray-selected broad-line active galactic nuclei (AGNs) at 0.6 &lt; z &lt; 1.7. We use 27 near-infrared spectra from the Fiber Multi-Object Spectrograph along with 26 sources from the literature. We show that the λ Edd and [N ii]λ6583/Hα ratio at 0.6 &lt; z &lt; 1.7 exhibits a similar anti-correlation distribution of λ Edd−[N ii]λ6583/Hα, as has been found for local ( ), ultra-hard, X-ray-selected AGNs. The observed distribution implies that there is a consistent relationship from local to z ∼ 1.7, which corresponds from the present time to 4 Gyr old. Further study of high-redshift, low-Eddington-ratio AGNs (log λ Edd &lt; −2) is necessary to determine fully whether the λ Edd−[N ii]λ6583/Hα anti-correlation still holds in high-redshift AGNs at low Eddington ratios.

The FMOS-COSMOS Survey of Star-forming Galaxies at z ∼ 1.6. VI. Redshift and Emission-line Catalog and Basic Properties of Star-forming Galaxies

Abstract We present a new data release from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS survey that contains the measurements of the spectroscopic redshift and flux of rest-frame optical emission lines (Hα, [N ii], [S ii], Hβ, [O iii]) for 1931 galaxies out of a total of 5484 objects observed over the 1.7 deg2 COSMOS field. We obtained H- and J-band medium-resolution (R ∼ 3000) spectra with FMOS mounted on the Subaru telescope, which offers an in-fiber line flux sensitivity limit of for an on-source exposure time of 5 hr. The full sample contains the main population of star-forming galaxies at z ∼ 1.6 over the stellar mass range , as well as other subsamples of infrared-luminous galaxies detected by Spitzer and Herschel at the same and lower (z ∼ 0.9) redshifts and X-ray-emitting galaxies detected by Chandra. This paper presents an overview of our spectral analyses, a description of the sample characteristics, and a summary of the basic properties of emission-line galaxies. We use the larger sample to redefine the stellar mass–star formation rate relation based on the dust-corrected Hα luminosity and find that the individual galaxies are better fit with a parameterization including a bending feature at M * ≈ 1010.2 M ⊙, and that the intrinsic scatter increases with M * from 0.19 to 0.37 dex. We also confirm with higher confidence that the massive (M * ≳ 1010.5 M ⊙) galaxies are chemically mature as much as local galaxies with the same stellar masses, and that the massive galaxies have lower [S ii]/Hα ratios for their [O iii]/Hβ as compared to local galaxies, which is indicative of enhancement in the ionization parameter.

THE FMOS-COSMOS SURVEY OF STAR-FORMING GALAXIES AT z ∼ 1.6. IV. EXCITATION STATE AND CHEMICAL ENRICHMENT OF THE INTERSTELLAR MEDIUM

ABSTRACT We investigate the physical conditions of ionized gas in high-z star-forming galaxies using diagnostic diagrams based on the rest-frame optical emission lines. The sample consists of 701 galaxies with an Hα detection at , from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS survey, that represent the normal star-forming population over the stellar mass range , with those at being well sampled. We confirm an offset of the average location of star-forming galaxies in the Baldwin–Phillips–Terlevich (BPT) diagram ( versus ), primarily toward higher , compared with local galaxies. Based on the [S ii] ratio, we measure an electron density ( ), which is higher than that of local galaxies. Based on comparisons to theoretical models, we argue that changes in emission-line ratios, including the offset in the BPT diagram, are caused by a higher ionization parameter both at fixed stellar mass and at fixed metallicity, with additional contributions from a higher gas density and possibly a hardening of the ionizing radiation field. Ionization due to active galactic nuclei is ruled out as assessed with Chandra. As a consequence, we revisit the mass–metallicity relation using and a new calibration including as recently introduced by Dopita et al. Consistent with our previous results, the most massive galaxies ( ) are fully enriched, while those at lower masses have metallicities lower than local galaxies. Finally, we demonstrate that the stellar masses, metallicities, and star formation rates of the FMOS sample are well fit with a physically motivated model for the chemical evolution of star-forming galaxies.

THE FMOS-COSMOS SURVEY OF STAR-FORMING GALAXIES AT z ∼ 1.6. III. SURVEY DESIGN, PERFORMANCE, AND SAMPLE CHARACTERISTICS

We present a spectroscopic survey of galaxies in the COSMOS field using the Fiber Multi-Object Spectrograph (FMOS), a near-infrared instrument on the Subaru Telescope. Our survey is specifically designed to detect the Halpha emission line that falls within the H-band (1.6-1.8 um) spectroscopic window from star-forming galaxies with 1.4 < z < 1.7 and M_stellar>~10^10 Msolar. With the high multiplex capability of FMOS, it is now feasible to construct samples of over one thousand galaxies having spectroscopic redshifts at epochs that were previously challenging. The high-resolution mode (R~2600) effectively separates Halpha and [NII]6585 thus enabling studies of the gas-phase metallicity and photoionization state of the interstellar medium. The primary aim of our program is to establish how star formation depends on stellar mass and environment, both recognized as drivers of galaxy evolution at lower redshifts. In addition to the main galaxy sample, our target selection places priority on those detected in the far-infrared by Herschel/PACS to assess the level of obscured star formation and investigate, in detail, outliers from the star formation rate - stellar mass relation. Galaxies with Halpha detections are followed up with FMOS observations at shorter wavelengths using the J-long (1.11-1.35 um) grating to detect Hbeta and [OIII]5008 that provides an assessment of extinction required to measure star formation rates not hampered by dust, and an indication of embedded Active Galactic Nuclei. With 460 redshifts measured from 1153 spectra, we assess the performance of the instrument with respect to achieving our goals, discuss inherent biases in the sample, and detail the emission-line properties. Our higher-level data products, including catalogs and spectra, are available to the community.

The Subaru FMOS galaxy redshift survey (FastSound). I. Overview of the survey targeting Hα emitters at z ∼ 1.4

Abstract FastSound is a galaxy redshift survey that uses the near-infrared Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru Telescope, targeting Hα emitters at z ∼ 1.18–1.54 down to the sensitivity limit of Hα flux ∼ 2 × 10−16 erg cm−2 s−1. The primary goal of the survey is to detect redshift space distortion (RSD), to test the general theory of relativity by measuring the growth rate of large-scale structure and to constrain modified gravity models for the origin of the accelerated expansion of the universe. The target galaxies were selected based on photometric redshifts and Hα flux estimates calculated by fitting spectral energy distribution (SED) models to the five optical magnitudes of the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) Wide catalog. The survey started in 2012 March, and all the observations were completed in 2014 July. In total, we achieved 121 pointings of FMOS (each pointing has a 30′ diameter circular footprint) covering 20.6 deg2 by tiling the four fields of the CFHTLS Wide in a hexagonal pattern. Emission lines were detected from ∼ 4000 star-forming galaxies by an automatic line detection algorithm applied to 2D spectral images. This is the first in a series of papers based on FastSound data, and we describe the details of the survey design, target selection, observations, data reduction, and emission line detections.

Physical conditions of the interstellar medium in star-forming galaxies at z ∼ 1.5

Abstract We present results from Subaru Fiber Multi Object Spectrograph near-infrared spectroscopy of 118 star-forming galaxies at z ∼ 1.5 in the Subaru Deep Field. These galaxies are selected as [O ii]λ3727 emitters at z ≈ 1.47 and 1.62 from narrow-band imaging. We detect the Hα emission line in 115 galaxies, the [O iii]λ5007 emission line in 45 galaxies, and Hβ, [N ii]λ6584, and [S ii]λλ6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O ii] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate the physical conditions of the interstellar medium in star-forming galaxies at z ∼ 1.5. We find a tight correlation between Hα and [O ii], which suggests that [O ii] can be a good star formation rate indicator for galaxies at z ∼ 1.5. The line ratios of Hα/[O ii] are consistent with those of local galaxies. We also find that [O ii] emitters have strong [O iii] emission lines. The [O iii]/[O ii] ratios are larger than normal star-forming galaxies in the local universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O iii]/[O ii] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

FIELD: Automated emission line detection software for Subaru/FMOS near-infrared spectroscopy

Abstract We describe the development of automated emission line detection software for the Fiber Multi-Object Spectrograph (FMOS), which is a near-infrared spectrograph fed by 400 fibers from the 0.2 deg2 prime focus field of view of the Subaru Telescope. The software, FIELD (FMOS software for Image-based Emission Line Detection), is developed and tested mainly for the FastSound survey, which is targeting Hα emitting galaxies at z ∼ 1.3 to measure the redshift space distortion as a test of general relativity beyond z ∼ 1. The basic algorithm is to calculate the line signal-to-noise ratio (S/N) along the wavelength direction, given by a 2D convolution of the spectral image and a detection kernel representing a typical emission line profile. A unique feature of FMOS is its use of OH airglow suppression masks, requiring the use of flat-field images to suppress noise around the mask regions. Bad pixels on the detectors and pixels affected by cosmic rays are efficiently removed using the information obtained from the FMOS analysis pipeline. We limit the range of acceptable line-shape parameters for the detected candidates to further improve the reliability of line detection. The final performance of line detection is tested using a subset of the FastSound data; the false detection rate of spurious objects is examined by using inverted frames obtained by exchanging object and sky frames. The false detection rate is &amp;lt; 1% at S/N &amp;gt; 5, allowing an efficient and objective emission line search for FMOS data at the line flux level of ≳ 1.0 × 10−16 erg cm−2 s−1.

The mass–metallicity relation at z ∼ 1.4 revealed with Subaru/FMOS★

We present a stellar mass–metallicity relation at z ∼ 1.4 with an unprecedentedly large sample of ∼340 star-forming galaxies obtained with Fibre Multi-Object Spectrograph (FMOS) on the Subaru Telescope. We observed K-band selected galaxies at 1.2 ≤ zph ≤ 1.6 in the Subaru XMM–Newton Deep Survey/Ultra Deep Survey fields with M* ≥ 109.5 M⊙, and expected F(Hα) ≥ 5 × 10−17 erg s−1 cm−2. Among the observed ∼1200 targets, 343 objects show significant Hα emission lines. The gas-phase metallicity is obtained from [N ii] λ6584/Hα line ratio, after excluding possible active galactic nuclei. Due to the faintness of the [N ii] λ6584 lines, we apply the stacking analysis and derive the mass–metallicity relation at z ∼ 1.4. Our results are compared to past results at different redshifts in the literature. The mass–metallicity relation at z ∼ 1.4 is located between those at z ∼ 0.8 and z ∼ 2.2; it is found that the metallicity increases with decreasing redshift from z ∼ 3 to z ∼ 0 at fixed stellar mass. Thanks to the large size of the sample, we can study the dependence of the mass–metallicity relation on various galaxy physical properties. The average metallicity from the stacked spectra is close to the local Fundamental Metallicity Relation (FMR) in the higher metallicity part but ≳ 0.1 dex higher in metallicity than the FMR in the lower metallicity part. We find that galaxies with larger E(B − V), B − R and R − H colours tend to show higher metallicity by ∼0.05 dex at fixed stellar mass. We also find relatively clearer size dependence that objects with smaller half-light radius tend to show higher metallicity by ∼0.1 dex at fixed stellar mass, especially in the low-mass part.

THE FMOS-COSMOS SURVEY OF STAR-FORMING GALAXIES AT z ∼ 1.6. I. Hα-BASED STAR FORMATION RATES AND DUST EXTINCTION

We present the first results from a near-IR spectroscopic survey of the COSMOS field, using the Fiber Multi-Object Spectrograph on the Subaru telescope, designed to characterize the star-forming galaxy population at $1.4<z<1.7$. The high-resolution mode is implemented to detect H$\alpha$ in emission between $1.6{\rm -}1.8 \mathrm{\mu m}$ with $f_{\rm H\alpha}\gtrsim4\times10^{-17}$ erg cm$^{-2}$ s$^{-1}$. Here, we specifically focus on 271 sBzK-selected galaxies that yield a H$\alpha$ detection thus providing a redshift and emission line luminosity to establish the relation between star formation rate and stellar mass. With further $J$-band spectroscopy for 89 of these, the level of dust extinction is assessed by measuring the Balmer decrement using co-added spectra. We find that the extinction ($0.6\lesssim A_\mathrm{H\alpha} \lesssim 2.5$) rises with stellar mass and is elevated at high masses compared to low-redshift galaxies. Using this subset of the spectroscopic sample, we further find that the differential extinction between stellar and nebular emission \hbox{$E_\mathrm{star}(B-V)/E_\mathrm{neb}(B-V)$} is 0.7--0.8, dissimilar to that typically seen at low redshift. After correcting for extinction, we derive an H$\alpha$-based main sequence with a slope ($0.81\pm0.04$) and normalization similar to previous studies at these redshifts.

A COMPARATIVE ANALYSIS OF VIRIAL BLACK HOLE MASS ESTIMATES OF MODERATE-LUMINOSITY ACTIVE GALACTIC NUCLEI USING SUBARU/FMOS

We present an analysis of broad emission lines observed in moderate-luminosity active galactic nuclei (AGNs), typical of those found in X-ray surveys of deep fields, with the aim to test the validity of single-epoch virial black hole mass estimates. We have acquired near-infrared (NIR) spectra of AGNs up to z ~ 1.8 in the COSMOS and Extended Chandra Deep Field-South Survey, with the Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru Telescope. These low-resolution NIR spectra provide a significant detection of the broad Halpha line that has been shown to be a reliable probe of black hole mass at low redshift. Our sample has existing optical spectroscopy which provides a detection of MgII, a broad emission line typically used for black hole mass estimation at z > 1. We carry out a spectral-line fitting procedure using both Halpha and MgII to determine the virial velocity of gas in the broad line region, the monochromatic continuum luminosity at 3000 A, and the total Halpha line luminosity. With a sample of 43 AGNs spanning a range of two decades in luminosity (i.e., L ~ 10^44-46 ergs/s), we find a tight correlation between the continuum and line luminosity with a distribution characterized by <log(L_3000/L_Halpha)> = 1.52 and a dispersion sigma = 0.16. There is also a close one-to-one relationship between the FWHM of Halpha and of MgII up to 10000 km/s with a dispersion of 0.14 in the distribution of the logarithm of their ratios. Both of these then lead to there being very good agreement between Halpha- and MgII-based masses over a wide range in black hole mass (i.e., M_BH ~ 10^7-9 M_sun). We do find a small offset in MgII-based masses, relative to those based on Halpha, of +0.17 dex and a dispersion sigma = 0.32. In general, these results demonstrate that local scaling relations, using MgII or Halpha, are applicable for AGN at moderate luminosities and up to z ~ 2.

FRD in optical fibres at low temperatures: investigations for Gemini's Wide-field Fibre Multi-Object Spectrograph

While there is no direct evidence for the deterioration in Focal Ratio Degradation (FRD) of optical fibres in severe temperature gradients, the fibre ends inserted into metallic containment devices such as steel ferrules can be a source of stress, and hence increased FRD at low temperatures. In such conditions, instruments using optical fibres may suffer some increase in FRD and consequent loss of system throughput when they are working in environments with significant thermal gradients, a common characteristic of ground-based observatories. In this paper we present results of experiments with optical fibres inserted in different materials as a part of our prototyping study for Gemini's Wide-field Multi-Object Spectrograph (WFMOS) project. Thermal effects and the use of new holding techniques will be discussed in the context of Integral Field Units and multi-fibres systems. In this work, we have used careful methodologies that give absolute measurements of FRD to quantify the advantages of using epoxy-based composites rather than metals as support structures for the fibre ends. This is shown to be especially important in minimizing thermally induced stresses in the fibre terminations. Not only is this important for optimizing fibre spectrograph performance but the benefits of using such materials are demonstrated in the minimization of positional variations and the avoidance of metal-to-glass delamination. Furthermore, by impregnating the composites with small zirconium oxide particles the composite materials supply their own fine polishing grit which aids significantly to the optical quality of the finished product.

Fibre Multi-Object Spectrograph (FMOS) for the Subaru Telescope

Fibre Multi-Object Spectrograph (FMOS) is the first near-infrared instrument with a wide field of view capable of acquiring spectra simultaneously from up to 400 objects. It has been developed as a common-use instrument for the F$/$2 prime-focus of the Subaru Telescope. The field coverage of 30$^\prime$ diameter is achieved using a new 3-element corrector optimized in the near-infrared (0.9–1.8$\ \mu$m) wavelength range. Due to limited space at the prime-focus, we have had to develop a novel fibre positioner, called “Echidna”, together with two OH-airglow suppressed spectrographs. FMOS consists of three subsystems: the prime focus unit for IR, the fibre positioning system/connector units, and the two spectrographs. After full systems integration, FMOS was installed on the telescope in late 2007. Many aspects of the performance were checked through various test and engineering observations. In this paper, we present the optical and mechanical components of FMOS, and show the results of our on-sky engineering observations to date.

Predicting spectral features in galaxy spectra from broad-band photometry

We explore the prospects of predicting emission-line features present in galaxy spectra given broad-band photometry alone. There is a general consent that colours, and spectral features, most notably the 4000 A break, can predict many properties of galaxies, including star formation rates and hence they could infer some of the line properties. We argue that these techniques have great prospects in helping us understand line emission in extragalactic objects and might speed up future galaxy redshift surveys if they are to target emission-line objects only. We use two independent methods, Artificial Neural Networks (based on the ANNz code) and Locally Weighted Regression (LWR), to retrieve correlations present in the colour N-dimensional space and to predict the equivalent widths present in the corresponding spectra. We also investigate how well it is possible to separate galaxies with and without lines from broad-band photometry only. We find, unsurprisingly, that recombination lines can be well predicted by galaxy colours. However, among collisional lines some can and some cannot be predicted well from galaxy colours alone, without any further redshift information. We also use our techniques to estimate how much information contained in spectral diagnostic diagrams can be recovered from broad-band photometry alone. We find that it is possible to classify active galactic nuclei and star formation objects relatively well using colours only. We suggest that this technique could be used to considerably improve redshift surveys such as the upcoming Fibre Multi Object Spectrograph (FMOS) survey and the planned Wide Field Multi Object Spectrograph (WFMOS) survey.

THE LATEST RESULTS FROM SUBARU TELESCOPE

The latest scientific highlights obtained with the Subaru telescope are given together with its current status and on-going instrumentation. We have been successfully operating the telescope and 8 observatory instruments (including an adaptive optics system) since January 1999, when the first light was accomplished. Open-use of Subaru began in December 2000. Subaru has a unique capability of its prime focus among other 8-10 meter class telescopes and has an excellent imaging performance as a result of its sophisticated active optics combined with the high stability of the sky at Mauna Kea. Scientific highlights are given on the discoveries of the most distant galaxies, spiral structure on a protoplanetary disk around AB Aur, and planetesimal belts in the debris disk around <TEX>$\beta$</TEX> Pic. Brief summaries are given for three new instruments: the Multi-Object Infrared Camera and Spectrograph (MOIRCS), 188 element adaptive optics system, and Fiber Multi-Object Spectrograph (FMOS)

ELID precision grinding of large special Schmidt plate for fibre multi-object spectrograph for 8.2 m Subaru telescope

To explore various scientific frontiers from nearby substellar objects to large scale structures of the high redshift universe, a Fibre Multi-Object Spectrograph (FMOS) is being developed as the second generation near-infrared measuring instrument for the prime focus of 8.2 m Subaru telescope in Hawaii, which employs a large special Schmidt plate element. The Schmidt plate consists of a large non-axisymmetric aspherical concave plate and a convex plate. This paper introduces its manufacturing process, focusing on its non-axisymmetric aspherical surface machining by utilizing synthetically ELID grinding and arc-enveloped grinding method. A new grinding system capable of fabricating large optical elements was developed with 10 nm resolution. In this ELID arc-enveloped grinding system, a Cast Iron Fibre Bonded (CIFB) diamond wheel was 3D controlled to scan the workpiece to generate required surface. Grinding characteristics such as attainable form accuracy, surface roughness were investigated. Furthermore, some measures to improve form accuracy were discussed and verified.