arXiv subjects

Fumihide Iwamuro

Publications and source records attributed to Fumihide Iwamuro.

At least 19 recordsLinked to original sources

arXiv2026

Assessing the Impact of Source Confusion for GREX-PLUS based on Deep JWST NIRCam Imaging

We investigate the effects of source confusion expected in observations with GREX-PLUS, a JAXA L-class space infrared telescope mission candidate with a wide-field infrared camera covering 2-8 um with a field of view of 0.50 deg$^2$. For the deep imaging band near 4 um, we calculate the GREX-PLUS PSF and ghost based on the latest optical design, and consider two representative imaging performance cases with PSF FWHM values of 0.9 and 1.2 arcsec. We construct simulated GREX-PLUS images at different depths by convolving JWST NIRCam imaging data from JADES, GLASS, CEERS, and COSMOS-Web with the PSF+ghost kernel. Comparing the limiting magnitudes estimated from random aperture photometry using the same aperture sizes, we find that the simulated GREX-PLUS images are shallower than the original JWST images, with larger deviations for deeper original JWST images. This likely reflects unresolved faint sources and extended PSF+ghost wings from bright sources, which elevate background fluctuations in blank regions. Nevertheless, the limiting magnitudes continue to improve with increasing integration time down to ~27 mag, without a clear plateau at depths comparable to the planned GREX-PLUS deep survey, although the improvement becomes progressively less efficient toward longer integrations. Based on Monte Carlo simulations, we estimate detection completeness and correct the number counts for magnitude bias and incompleteness, finding that confusion-induced blending can reduce the completeness even at magnitudes well above the nominal 5-sigma depth. The completeness-corrected number counts agree well with the JWST-based number counts down to around the detection limit. Overall, our results suggest that statistical studies of faint galaxies remain feasible for GREX-PLUS; however, survey planning should account for less efficient depth improvement toward longer integrations due to source confusion.

astro-ph.GA↗

arXiv2024

Probing the origin of the two-component structure of broad line region by reverberation mapping of an extremely variable quasar

The physical origins of quasar components, such as the broad line region (BLR) and dust torus, remain under debate. To gain insights into them, we focused on Changing-State Quasars (CSQs) which provide a unique perspective through structural changes associated with accretion disk state transitions. We targeted SDSS J125809.31+351943.0, an extremely variable CSQ, to study its central core structure and kinematics. We conducted reverberation mapping with optical spectroscopy to explore the structure of the BLR and estimate the black hole mass. The results from H$β$ reverberation mapping indicated a black hole mass of $10^{9.64^{+0.11}_{-0.20}}\rm{M_\odot}$. Additionally, we analyzed variations in the optical to X-ray spectral indices, $α_{\rm{ox}}$, before and after the state transition, to investigate the accretion disk. These variations in $α_{\rm{ox}}$ and the Eddington ratio (from 0.4 \% to 2.4 \%) exhibitied behavior similar to state transitions observed in X-ray binary systems. Spectral analysis of H$β$ revealed a predominantly double-peaked profile during dim periods, transitioning to include a single-peaked component as the quasar brightened, suggesting that H$β$ contains a mixture of two components. Each of these components has its distinct characteristics: the first is a double-peaked profile that remains stable despite changes in the accretion rate, while the second is a variable single-peaked profile. Using time lags from reverberation mapping, we estimated the spatial relationships between these BLR components, the accretion disk, and the dust torus. Our results suggest that the BLR consists of two distinct components, each differing in location and origin.

astro-ph.GA↗

arXiv2022

The relation between quasars' optical spectra and variability

This work aimed to find the relationship between quasars' optical variability and spectral features to reveal the regularity behind the random variation. It is known that quasar's FeII/Hbeta flux ratio and equivalent width of [OIII]5007 are negatively correlated, called Eigenvector 1. In this work, we visualized the relationship between the position on this Eigenvector 1 (EV1) plane and how they had changed their brightness after ~10 years. We conducted three analyses using different quasar samples each. The first analysis showed the relation between their distributions on the EV1 plane and how much they had changed brightness, using 13,438 Sloan Digital Sky Survey quasars. This result shows how brightness changes later are clearly related to the position on the EV1 plane. In the second analysis, we plotted the sources reported as Changing-Look(State) Quasars on the EV1 plane. This result shows that the position on the EV1 plane corresponds activity level of each source, the bright or dim state of them are distributed on the opposite sides divided by the typical quasar distribution. In the third analysis, we examined the transition vectors on the EV1 plane using sources with multiple-epoch spectra. This result shows that the brightening and dimming sources move on the similar path and they turn into the position corresponding to the opposite activity level. We also found this trend is opposite to the empirical rule that RFeII positively correlated with the Eddington ratio, which has been proposed based on the trends of a large number of quasars. From all these analyses, it is indicated that quasars tend to oscillate between both sides of the distribution ridge on the EV1 plane; each of them corresponds to a dim state and a bright state. This trend in optical variation suggests that significant brightness changes, such as Changing-Look quasars, are expected to repeat.

astro-ph.GA↗

arXiv2022

Discovery of a new extreme changing-state quasar with 4 mag variation, SDSS J125809.31+351943.0

We report the discovery of a quasar, SDSS J125809.31+351943.0 (J1258), which brightened in optical for 4 mag from 1983 to 2015, which is one of the largest quasar brightening events so far. The history of optical photometry data of this quasar from the Catalina Real-time Transient Survey and All Sky Automated Survey for Super Novae (ASAS-SN), mid-infrared photometry data from the WISE satellite, and the broad emission line (BEL) flux obtained by spectroscopy of Sloan Digital Sky Survey shows their significant increases between 2003 and 2015. Investigating its CFHT photometric observations in 1983 and the USNO-B catalog, which contains data in 1975 and 1969, we found that the source was 4 mag fainter before than the peak of the recent ASAS-SN photometry. From the history of these data, we identified J1258 as a new Changing-State Quasar (CSQ; or Changing-Look Quasar). We also performed follow-up spectroscopic observations in December 2018 and May 2019, using the 2-meter telescope in Nishi-Harima Astronomical Observatory. The results show that the continuum flux and the BEL flux decreased to about 50 % of its peak. This indicates that J1258 is causing two changing-states for the BEL flux and continuum flux. We argue that J1258's variability, especially its brightening event, can be explained by the propagation of the heating front and the accretion disk state transitions based on the timescale and Eddington ratio variations. The estimated mass of the black hole of J1258 is about an order of magnitude larger than the CSQs found so far. Since both the changing timescale and the size of the accretion disk depend on the black hole mass, the J1258 brightening event can be interpreted as a scaled version of the variability in other CSQs. This suggests that samples of distant quasars with larger black hole masses may contain objects with longer and severer variations.

astro-ph.GA↗

arXiv2019

KOOLS--IFU: Kyoto Okayama Optical Low-dispersion Spectrograph with Optical-Fiber Integral Field Unit

Observations of transient objects, such as short gamma-ray bursts (GRBs) and electromagnetic counterparts of gravitational wave sources, require prompt spectroscopy. To carry out prompt spectroscopy, we developed an optical-fiber integral field unit (IFU) and connected it with an existing optical spectrograph KOOLS. KOOLS with IFU, hereafter KOOLS--IFU, was mounted on the Okayama Astrophysical Observatory 188-cm telescope. The fiber core and cladding diameters of the fiber bundle are 100 $μ$m and 125 $μ$m, respectively, and 127 fibers are hexagonally close-packed in the sleeve of the two-dimensional (2D) fiber array. We conducted test observations to measure the KOOLS--IFU performance and obtained the following conclusions: (1) the spatial sampling is 2''.34 $\pm$ 0''.05 per fiber, and the total field of view (FoV) is 30''.4 $\pm$ 0''.65 with 127 fibers; (2) the observable wavelength and the spectral resolving power of the grisms of KOOLS are 4030--7310 A and 400--600; 5020--8830 A and 600--900; 4160--6000 A and 1000--1200; and 6150--7930 A and 1800--2400, respectively; and (3) the estimated limiting magnitude is 18.2--18.7 AB mag during 30-min exposure under the optimal condition.

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arXiv2016

Constraint on the inflow/outflow rates in star-forming galaxies at z~1.4 from molecular gas observations

We constrain the rate of gas inflow into and outflow from a main-sequence star-forming galaxy at z~1.4 by fitting a simple analytic model for the chemical evolution in a galaxy to the observational data of the stellar mass, metallicity, and molecular gas mass fraction. The molecular gas mass is derived from CO observations with a metallicity-dependent CO-to-H2 conversion factor, and the gas metallicity is derived from the Hα and [NII]λ 6584 emission line ratio. Using a stacking analysis of CO integrated intensity maps and the emission lines of Hα and [NII], the relation between stellar mass, metallicity, and gas mass fraction is derived. We constrain the inflow and outflow rates with least-chi-square fitting of a simple analytic chemical evolution model to the observational data. The best-fit inflow and outflow rates are ~1.7 and ~0.4 in units of star-formation rate, respectively. The inflow rate is roughly comparable to the sum of the star-formation rate and outflow rate, which supports the equilibrium model for galaxy evolution; i.e., all inflow gas is consumed by star formation and outflow.

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arXiv2016

The Subaru FMOS Galaxy Redshift Survey (FastSound). II. The Emission Line Catalog and Properties of Emission Line Galaxies

We present basic properties of $\sim$3,300 emission line galaxies detected by the FastSound survey, which are mostly H$α$ emitters at $z \sim$ 1.2-1.5 in the total area of about 20 deg$^2$, with the H$α$ flux sensitivity limit of $\sim 1.6 \times 10^{-16} \rm erg \ cm^{-2} s^{-1}$ at 4.5 sigma. This paper presents the catalogs of the FastSound emission lines and galaxies, which will be open to the public in the near future. We also present basic properties of typical FastSound H$α$ emitters, which have H$α$ luminosities of $10^{41.8}$-$10^{43.3}$ erg/s, SFRs of 20--500 $M_\odot$/yr, and stellar masses of $10^{10.0}$--$10^{11.3}$ $M_\odot$. The 3D distribution maps for the four fields of CFHTLS W1--4 are presented, clearly showing large scale clustering of galaxies at the scale of $\sim$ 100--600 comoving Mpc. Based on 1,105 galaxies with detections of multiple emission lines, we estimate that contamination of non-H$α$ lines is about 4% in the single-line emission galaxies, which are mostly [OIII]$λ$5007. This contamination fraction is also confirmed by the stacked spectrum of all the FastSound spectra, in which H$α$, [NII]$λλ$6548,6583, [SII]$λλ$6717, 6731, and [OI]$λλ$6300,6364 are seen.

astro-ph.GA↗

arXiv2016

The Subaru FMOS galaxy redshift survey (FastSound). IV. New constraint on gravity theory from redshift space distortions at $z\sim 1.4$

We measure the redshift-space correlation function from a spectroscopic sample of 2783 emission line galaxies from the FastSound survey. The survey, which uses the Subaru Telescope and covers the redshift ranges of $1.19<z<1.55$, is the first cosmological study at such high redshifts. We detect clear anisotropy due to redshift-space distortions (RSD) both in the correlation function as a function of separations parallel and perpendicular to the line of sight and its quadrupole moment. RSD has been extensively used to test general relativity on cosmological scales at $z<1$. Adopting a LCDM cosmology with the fixed expansion history and no velocity dispersion $σ_{\rm v}=0$, and using the RSD measurements on scales above 8Mpc/h, we obtain the first constraint on the growth rate at the redshift, $f(z)σ_8(z)=0.482\pm 0.116$ at $z\sim 1.4$ after marginalizing over the galaxy bias parameter $b(z)σ_8(z)$. This corresponds to $4.2σ$ detection of RSD. Our constraint is consistent with the prediction of general relativity $fσ_8\sim 0.392$ within the $1-σ$ confidence level. When we allow $σ_{\rm v}$ to vary and marginalize it over, the growth rate constraint becomes $fσ_8=0.494^{+0.126}_{-0.120}$. We also demonstrate that by combining with the low-z constraints on $fσ_8$, high-z galaxy surveys like the FastSound can be useful to distinguish modified gravity models without relying on CMB anisotropy experiments.

astro-ph.CO↗

arXiv2016

Properties of the Interstellar Medium in Star-Forming Galaxies at z~1.4 revealed with ALMA

We conducted observations of 12CO(J=5-4) and dust thermal continuum emission toward twenty star-forming galaxies on the main sequence at z~1.4 using ALMA to investigate the properties of the interstellar medium. The sample galaxies are chosen to trace the distributions of star-forming galaxies in diagrams of stellar mass-star formation rate and stellar mass-metallicity. We detected CO emission lines from eleven galaxies. The molecular gas mass is derived by adopting a metallicity-dependent CO-to-H2 conversion factor and assuming a CO(5-4)/CO(1-0) luminosity ratio of 0.23. Molecular gas masses and its fractions (molecular gas mass/(molecular gas mass + stellar mass)) for the detected galaxies are in the ranges of (3.9-12) x 10^{10} Msun and 0.25-0.94, respectively; these values are significantly larger than those in local spiral galaxies. The molecular gas mass fraction decreases with increasing stellar mass; the relation holds for four times lower stellar mass than that covered in previous studies, and that the molecular gas mass fraction decreases with increasing metallicity. Stacking analyses also show the same trends. The dust thermal emissions were clearly detected from two galaxies and marginally detected from five galaxies. Dust masses of the detected galaxies are (3.9-38) x 10^{7} Msun. We derived gas-to-dust ratios and found they are 3-4 times larger than those in local galaxies. The depletion times of molecular gas for the detected galaxies are (1.4-36) x 10^{8} yr while the results of the stacking analysis show ~3 x 10^{8} yr. The depletion time tends to decrease with increasing stellar mass and metallicity though the trend is not so significant, which contrasts with the trends in local galaxies.

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arXiv2015

The Subaru FMOS Galaxy Redshift Survey (FastSound). III. The mass-metallicity relation and the fundamental metallicity relation at $z\sim1.4$

We present the results from a large near-infrared spectroscopic survey with Subaru/FMOS (\textit{FastSound}) consisting of $\sim$ 4,000 galaxies at $z\sim1.4$ with significant H$α$ detection. We measure the gas-phase metallicity from the [N~{\sc ii}]$λ$6583/H$α$ emission line ratio of the composite spectra in various stellar mass and star-formation rate bins. The resulting mass-metallicity relation generally agrees with previous studies obtained in a similar redshift range to that of our sample. No clear dependence of the mass-metallicity relation with star-formation rate is found. Our result at $z\sim1.4$ is roughly in agreement with the fundamental metallicity relation at $z\sim0.1$ with fiber aperture corrected star-formation rate. We detect significant [S~{\sc ii}]$λλ$6716,6731 emission lines from the composite spectra. The electron density estimated from the [S~{\sc ii}]$λλ$6716,6731 line ratio ranges from 10 -- 500 cm$^{-3}$, which generally agrees with that of local galaxies. On the other hand, the distribution of our sample on [N~{\sc ii}]$λ$6583/H$α$ vs. [S~{\sc ii}]$λλ$6716,6731/H$α$ is different from that found locally. We estimate the nitrogen-to-oxygen abundance ratio (N/O) from the N2S2 index, and find that the N/O in galaxies at $z\sim1.4$ is significantly higher than the local values at a fixed metallicity and stellar mass. The metallicity at $z\sim1.4$ recalculated with this N/O enhancement taken into account decreases by 0.1 -- 0.2 dex. The resulting metallicity is lower than the local fundamental metallicity relation.

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arXiv2015

The Subaru-XMM-Newton Deep Survey (SXDS) VIII.: Multi-wavelength Identification, Optical/NIR Spectroscopic Properties, and Photometric Redshifts of X-ray Sources

We report the multi-wavelength identification of the X-ray sources found in the Subaru-XMM-Newton Deep Survey (SXDS) using deep imaging data covering the wavelength range between the far-UV to the mid-IR. We select a primary counterpart of each X-ray source by applying the likelihood ratio method to R-band, 3.6micron, near-UV, and 24micron source catalogs as well as matching catalogs of AGN candidates selected in 1.4GHz radio and i'-band variability surveys. Once candidates of Galactic stars, ultra-luminous X-ray sources in a nearby galaxy, and clusters of galaxies are removed there are 896 AGN candidates in the sample. We conduct spectroscopic observations of the primary counterparts with multi-object spectrographs in the optical and NIR; 65\% of the X-ray AGN candidates are spectroscopically-identified. For the remaining X-ray AGN candidates, we evaluate their photometric redshift with photometric data in 15 bands. Utilising the multi-wavelength photometric data of the large sample of X-ray selected AGNs, we evaluate the stellar masses, M*, of the host galaxies of the narrow-line AGNs. The distribution of the stellar mass is remarkably constant from z=0.1 to 4.0. The relation between M* and 2--10 keV luminosity can be explained with strong cosmological evolution of the relationship between the black hole mass and M*. We also evaluate the scatter of the UV-MIR spectral energy distribution (SED) of the X-ray AGNs as a function of X-ray luminosity and absorption to the nucleus. The scatter is compared with galaxies which have redshift and stellar mass distribution matched with the X-ray AGN. The UV-NIR SEDs of obscured X-ray AGNs are similar to those of the galaxies in the matched sample. In the NIR-MIR range, the median SEDs of X-ray AGNs are redder, but the scatter of the SEDs of the X-ray AGN broadly overlaps that of the galaxies in the matched sample.

astro-ph.GA↗

arXiv2015

The Subaru FMOS Galaxy Redshift Survey (FastSound). I. Overview of the Survey Targeting on H$α$ Emitters at $z \sim 1.4$

FastSound is a galaxy redshift survey using the near-infrared Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru Telescope, targeting H$α$ emitters at $z \sim 1.18$--$1.54$ down to the sensitivity limit of H$α$ flux $\sim 2 \times 10^{-16} \ \rm erg \ cm^{-2} s^{-1}$. The primary goal of the survey is to detect redshift space distortions (RSD), to test General 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 H$α$ 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 March 2012, and all the observations were completed in July 2014. In total, we achieved $121$ pointings of FMOS (each pointing has a $30$ arcmin diameter circular footprint) covering $20.6$ deg$^2$ by tiling the four fields of the CFHTLS Wide in a hexagonal pattern. Emission lines were detected from $\sim 4,000$ 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.

astro-ph.CO↗

arXiv2014

The gas inflow and outflow rate in star-forming galaxies at $z\sim1.4$

We try to constrain the gas inflow and outflow rate of star-forming galaxies at $z\sim1.4$ by employing a simple analytic model for the chemical evolution of galaxies. The sample is constructed based on a large near-infrared (NIR) spectroscopic sample observed with Subaru/FMOS. The gas-phase metallicity is measured from the [\ion{N}{2}]$λ$6584/H$α$ emission line ratio and the gas mass is derived from the extinction corrected H$α$ luminosity by assuming the Kennicutt-Schmidt law. We constrain the inflow and outflow rate from the least-$χ^{2}$ fittings of the observed gas mass fraction, stellar mass, and metallicity with the analytic model. The joint $χ^{2}$ fitting shows the best-fit inflow rate is $\sim1.8$ and the outflow rate is $\sim0.6$ in unit of star-formation rate (SFR). By applying the same analysis to the previous studies at $z\sim0$ and $z\sim2.2$, it is shown that the both inflow rate and outflow rate decrease with decreasing redshift, which implies the higher activity of gas flow process at higher redshift. The decreasing trend of the inflow rate from $z\sim2.2$ to $z\sim0$ agrees with that seen in the previous observational works with different methods, though the absolute value is generally larger than the previous works. The outflow rate and its evolution from $z\sim2.2$ to $z\sim0$ obtained in this work agree well with the independent estimations in the previous observational works.

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arXiv2014

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

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 $0.2$ deg$^2$ 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 H$α$ emitting galaxies at $z \sim 1.3$ to measure the redshift space distortion as a test of general relativity beyond $z \sim 1$. The basic algorithm is to calculate the line signal-to-noise ratio ($S/N$) along the wavelength direction, given by a 2-D 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 by 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 $< 1$\% at $S/N > 5$, allowing an efficient and objective emission line search for FMOS data at the line flux level of $\gtrsim 1.0 \times 10^{-16}$[erg/cm$^2$/s].

astro-ph.IM↗

arXiv2013

A Study of Selection Methods for H alpha Emitting Galaxies at z~1.3 for the Subaru/FMOS Galaxy Redshift Survey for Cosmology (FastSound)

The efficient selection of high-redshift emission galaxies is important for future large galaxy redshift surveys for cosmology. Here we describe the target selection methods for the FastSound project, a redshift survey for H alpha emitting galaxies at z=1.2-1.5 using Subaru/FMOS to measure the linear growth rate fσ8 via Redshift Space Distortion (RSD) and constrain the theory of gravity. To select ~400 target galaxies in the 0.2 deg^2 FMOS field-of-view from photometric data of CFHTLS-Wide (u*g'r'i'z'), we test several different methods based on color-color diagrams or photometric redshift estimates from spectral energy distribution (SED) fitting. We also test the improvement in selection efficiency that can be achieved by adding near-infrared data from the UKIDSS DXS (J). The success rates of H alpha detection with FMOS averaged over two observed fields using these methods are 11.3% (color-color, optical), 13.6% (color-color, optical+NIR), 17.3% (photo-z, optical), and 15.1% (photo-z, optical+NIR). Selection from photometric redshifts tends to give a better efficiency than color-based methods, although there is no significant improvement by adding J band data within the statistical scatter. We also investigate the main limiting factors for the success rate, by using the sample of the HiZELS H alpha emitters that were selected by narrow-band imaging. Although the number density of total H alpha emitters having higher H alpha fluxes than the FMOS sensitivity is comparable with the FMOS fiber density, the limited accuracy of photometric redshift and H alpha flux estimations have comparable effects on the success rate of <~20% obtained from SED fitting.

astro-ph.CO↗

arXiv2013

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 FMOS on the Subaru Telescope. We observed K-band selected galaxies at 1.2 < z_{ph} < 1.6 in the SXDS/UDS fields with M_{*} > 10^{9.5} M_{\sun}, and expected F(Hα) > 5 \times 10^{-17} erg s^{-1} cm^{-2}. Among the observed ~1200 targets, 343 objects show significant Hαemission lines. The gas-phase metallicity is obtained from [NII]λ6584/Hαline ratio, after excluding possible active galactic nuclei (AGNs). Due to the faintness of the [NII]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 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.

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arXiv2011

NIR Spectroscopy of Star-Forming Galaxies at z~1.4 with Subaru/FMOS: The Mass-Metallicity Relation

We present near-infrared spectroscopic observations of star-forming galaxies at z~1.4 with FMOS on the Subaru Telescope. We observed K-band selected galaxies in the SXDS/UDS fields with K<23.9 mag, 1.2 10^{9.5} Msun, and expected F(Halpha)>10^{-16} erg s^{-1} cm^{-2}. 71 objects in the sample have significant detections of Halpha. For these objects, excluding possible AGNs identified from the BPT diagram, gas-phase metallicities are obtained from [NII]/Halpha line ratio. The sample is split into three stellar mass bins, and the spectra are stacked in each stellar mass bin. The mass-metallicity relation obtained at z~1.4 is located between those at z~0.8 and z~2.2. We constrain an intrinsic scatter to be ~0.1 dex or larger in the mass-metallicity relation at z~1.4; the scatter may be larger at higher redshifts. We found trends that the deviation from the mass-metallicity relation depends on the SFR and the half light radius: Galaxies with higher SFR and larger half light radii show lower metallicities at a given stellar mass. One possible scenario for the trends is the infall of pristine gas accreted from IGM or through merger events. Our data points show larger scatter than the fundamental metallicity relation (FMR) at z~0.1 and the average metallicities slightly deviate from the FMR. The compilation of the mass-metallicity relations at z~3 to z~0.1 shows that they evolve smoothly from z~3 to z~0 without changing the shape so much except for the massive part at z~0.

astro-ph.CO↗

arXiv2010

The Fibre Multi-Object Spectrograph (FMOS) for 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' diameter is achieved using a new 3-element corrector optimized in the near-infrared (0.9-1.8um) 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 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.

astro-ph.IM↗