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Search Results: 1 - 10 of 445 matches for " Masami Ouchi "
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Ionization State of Inter-Stellar Medium in Galaxies: Evolution, SFR-M_star-Z Dependence, and Ionizing Photon Escape
Kimihiko Nakajima,Masami Ouchi
Physics , 2013, DOI: 10.1093/mnras/stu902
Abstract: We present a systematic study for ionization state of inter-stellar medium in galaxies at z=0-3 with ~140,000 SDSS galaxies and 108 intermediate to high redshift galaxies from the literature, using an ionization-parameter sensitive line ratio of [OIII]5007/[OII]3727 and photoionization models. We confirm that z=2-3 galaxies show an [OIII]/[OII] ratio significantly higher than a typical star-forming galaxy of SDSS by a factor of >~10, and the photoionization models reveal that these high-z galaxies have an ionization parameter of log(qion/cm s^{-1})~7.6-9.0, a factor of ~4-10 higher than local galaxies. For galaxies at any redshift, we identify a correlation between the [OIII]/[OII] ratio and galaxy global properties of star-formation rate (SFR), stellar mass (M_star), and metallicity (Z). We extend the fundamental metallicity relation (FMR) and develop the fundamental ionization relation (FIR), a four-dimensional relation of ionization parameter, SFR, M_star, and Z. The intermediate and high-z galaxies up to z~3 follow the FIR defined with the local galaxies, in contrast with the FMR whose possible evolution from z~2 to 3 is reported. We find that the FMR evolution of z~2-3 appears, if one omits ionization parameter differences, and that the FMR evolution does not exist for an average metallicity solution of z~3 galaxies with a high-ionization parameter. Interestingly, all of two local Lyman-continuum emitting galaxies (LyC leakers) have a high [OIII]/[OII] ratio, indicating a positive correlation between [OIII]/[OII] and ionizing photon escape fraction (fesc), which is successfully explained by our photoionization models. Because [OIII]/[OII] ratios of z~2-3 galaxies, especially Ly-alpha emitters (LAEs), are comparable to, or higher than, those of the local LyC leakers, these high-z galaxies are candidates of Lyman-continuum emitting objects. (abridged)
Morphologies of ~190,000 Galaxies at z=0-10 Revealed with HST Legacy Data I. Size Evolution
Takatoshi Shibuya,Masami Ouchi,Yuichi Harikane
Physics , 2015,
Abstract: We present redshift evolution of galaxy effective radius r_e obtained from the HST samples of ~190,000 galaxies at z=0-10. Our HST samples consist of 176,152 photo-z galaxies at z=0-6 from the 3D-HST+CANDELS catalogue and 10,454 LBGs at z=4-10 identified in CANDELS, HUDF09/12, and HFF parallel fields, providing the largest data set to date for galaxy size evolution studies. We derive r_e with the same technique over the wide-redshift range of z=0-10, evaluating the optical-to-UV morphological K-correction and the selection bias of photo-z galaxies+LBGs as well as the cosmological surface brightness dimming effect. We find that r_e values at a given luminosity significantly decrease towards high-z, regardless of statistics choices. For star-forming galaxies, there is no evolution of the power-law slope of the size-luminosity relation and the median Sersic index (n~1.5). Moreover, the r_e-distribution is well represented by log-normal functions whose standard deviation \sigma_{\ln{r_e}} does not show significant evolution within the range of \sigma_{\ln{r_e}}~0.45-0.75. We calculate the stellar-to-halo size ratio from our r_e measurements and the dark-matter halo masses estimated from the abundance matching study, and obtain a nearly constant value of r_e/r_vir=1.0-3.5% at z=0-8. The combination of the r_e-distribution shape+standard deviation, the constant r_e/r_vir, and n~1.5 suggests a picture that typical high-z star-forming galaxies have disk-like stellar components in a sense of dynamics and morphology over cosmic time of z~0-6. If high-z star-forming galaxies are truly dominated by disks, the r_e/r_vir value and the disk formation model indicate that the specific angular momentum of the disk normalized by the host halo is j_d/m_d=0.5-1. These are statistical results for galaxies' major stellar components, and the detailed study of clumpy sub-components is presented in the paper II.
Very Compact Dense Galaxy Overdensity with δ ~ 130 Identified at z ~ 8: Implications for Early Protocluster and Cluster-Core Formation
Masafumi Ishigaki,Masami Ouchi,Yuichi Harikane
Physics , 2015,
Abstract: We report the first identification of a compact dense galaxy overdensity at $z\sim 8$ dubbed A2744z8OD. A2744z8OD consists of eight $Y$-dropout galaxies behind Abell 2744 that is originally pinpointed by Hubble Frontier Fields studies. However, no studies have, so far, derived basic physical quantities of structure formation or made comparisons with theoretical models. We obtain a homogeneous sample of dropout galaxies at $z\sim 8$ from eight field data of Hubble legacy images that are as deep as the A2744z8OD data. Using the sample, we find that a galaxy surface overdensity value of A2744z8OD is very high $\delta\simeq 130$ that is defined in a small circle of $6"$ ($\simeq 30$ physical kpc) radius. Because there is no such a large $\delta$ value reported for high-$z$ overdensities to date, A2744z8OD is a system clearly different from those found in previous high-$z$ overdensity studies. The total stellar mass of A2744z8OD is estimated to be $3.8\times 10^9 M_\odot$ that is as small as today's Large Magellanic Cloud. In the galaxy+structure formation models of Henriques et al. (2015), there exist a very similar overdensity, Modelz8OD, that is made of eight model dropout galaxies at $z\sim 8$ in a $6"$-radius circle. Eight out of seven galaxies in Modelz8OD form a filament within $\Delta z \sim 0.03$ that is elongated in the line of sight, which enhance $\delta$ of Modelz8OD. Modelz8OD is a progenitor of a today's cluster with $10^{14} M_\odot$, and more than a half of the seven Modelz8OD galaxies are merged into the brightest cluster galaxy (BCG) in the today's cluster. If Modelz8OD is a counterpart of A2744z8OD, the models suggest that A2744z8OD would be a forming cluster core of a today's $10^{14} M_\odot$ cluster that started formation earlier than the most of the other BCG progenitors at $z>12$.
The sizes of $z\sim6-8$ lensed galaxies from the Hubble Frontier Fields Abell 2744 data
Ryota Kawamata,Masafumi Ishigaki,Kazuhiro Shimasaku,Masamune Oguri,Masami Ouchi
Physics , 2014, DOI: 10.1088/0004-637X/804/2/103
Abstract: We investigate sizes of $z\sim6-8$ dropout galaxies using the complete data of the Abell 2744 cluster and parallel fields in the Hubble Frontier Fields program. By directly fitting light profiles of observed galaxies with lensing-distorted S\'ersic profiles on the image plane with the \texttt{glafic} software, we accurately measure intrinsic sizes of 31 $z\sim6-7$ and eight $z\sim8$ galaxies, including those as faint as $M_{\mathrm{UV}}\simeq-16.6$. We find that half-light radii $r_\mathrm{e}$ positively correlates with UV luminosity at each redshift, although the correlation is not very tight. Largest ($r_\mathrm{e}>0.8$ kpc) galaxies are mostly red in UV color while smallest ($r_\mathrm{e} < 0.08$ kpc) ones tend to be blue. We also find that galaxies with multiple cores tend to be brighter. Combined with previous results at $2.5\lesssim z\lesssim12$, our result confirms that the average $r_{\mathrm{e}}$ of bright ($(0.3-1)L^\star_{z=3}$) galaxies scales as $r_{\mathrm{e}}\propto(1+z)^{-m}$ with $m=1.24\pm0.1$. We find that the ratio of $r_\mathrm{e}$ to virial radius is virtually constant at $3.3\pm0.1\%$ over a wide redshift range, where the virial radii of hosting dark matter halos are derived based on the abundance matching. This constant ratio is consistent with the disk formation model by Mo et al. (1998) with $j_\mathrm{d}\sim m_\mathrm{d}$, where $j_\mathrm{d}$ and $m_\mathrm{d}$ are the fractions of the angular momentum and mass within halos confined in the disks. A comparison with various types of local galaxies indicates that our galaxies are most similar to circumnuclear star-forming regions of barred galaxies in the sense that a sizable amount of stars are forming in a very small area.
Properties of host haloes of Lyman-break galaxies and Lyman-alpha Emitters from their number densities and angular clustering
Takashi Hamana,Masami Ouchi,Kazuhiro Shimasaku,Issha Kayo,Yasushi Suto
Physics , 2003, DOI: 10.1111/j.1365-2966.2004.07253.x
Abstract: We explore empirical relations between three different populations of high-redshift galaxies and their hosting dark halos employing the halo model approach. Specifically we consider Lyman-break galaxies at z\sim4 and at z\sim5, and Lyman-Alpha emitters at z\simeq 4.86. We adopt a halo occupation function prescription to parameterize the properties of their hosting halos and the efficiency of halo-dependent star formation. We find that the two LBG samples are well described by the halo model with an appropriate HOF. We obtain constraints on properties of their hosting halos. A typical mass of hosting halos for LBGs is 5\times10^{11}h^{-1}M_\odot and the expected number of LBGs per halo is \sim0.5, therefore there is an approximate one-to-one correspondence between halos and LBGs. We also find a sign of the minimum mass of LBG hosting halos decreasing with time. We discuss implications of these findings on the star formation history of LBGs. On the other hand, for LAEs, our simple HOF prescription fails to reproduce simultaneously the observed angular correlation function and the number density. This might imply either that the distribution of LAEs within hosting halos differs from that of dark matter, or that the strong large-scale correlation is due to the existence of an unusual, large overdense region, and so the survey region is not a representative of the z\sim5 universe, the definite answer should wait for a much wider survey of LAEs at high redshifts.
Keck Spectroscopy of Faint 3
Daniel P. Stark,Richard S. Ellis,Masami Ouchi
Physics , 2010, DOI: 10.1088/2041-8205/728/1/L2
Abstract: As Lyman-alpha photons are scattered by neutral hydrogen, a change with redshift in the Lyman-alpha equivalent width distribution of distant galaxies offers a promising probe of the degree of ionization in the intergalactic medium and hence when cosmic reionization ended. This simple test is complicated by the fact that Lyman-alpha emission can also be affected by the evolving astrophysical details of the host galaxies. In the first paper in this series, we demonstrated both a luminosity and redshift dependent trend in the fraction of Lyman-alpha emitters seen within color-selected Lyman-break galaxies (LBGs) over the range 325 A) emission, an increase of 1.6x from a similar sample observed at z~4. With a total sample of 74 z~6 LBGs, we determine the luminosity-dependent Lyman-alpha equivalent width distribution. Assuming continuity in these trends to the new population of z~7 sources located with the Hubble WFC3/IR camera, we predict that unless the neutral fraction rises in the intervening 200 Myr, the success rate for spectroscopic confirmation using Lyman-alpha emission should be high.
Faint Submillimeter Galaxies Revealed by Multifield Deep ALMA Observations: Number Counts, Spatial Clustering, and A Dark Submillimeter Line Emitter
Yoshiaki Ono,Masami Ouchi,Yasutaka Kurono,Rieko Momose
Physics , 2014, DOI: 10.1088/0004-637X/795/1/5
Abstract: We present the statistics of faint submillimeter/millimeter galaxies (SMGs) and serendipitous detections of a submillimeter/millimeter line emitter (SLE) with no multi-wavelength continuum counterpart revealed by the deep ALMA observations. We identify faint SMGs with flux densities of 0.1-1.0 mJy in the deep Band 6 and Band 7 maps of 10 independent fields that reduce cosmic variance effects. The differential number counts at 1.2 mm are found to increase with decreasing flux density down to 0.1 mJy. Our number counts indicate that the faint (0.1-1.0 mJy, or SFR_IR ~ 30-300 Msun/yr) SMGs contribute nearly a half of the extragalactic background light (EBL), while the remaining half of the EBL is mostly contributed by very faint sources with flux densities of <0.1 mJy (SFR_IR <~ 30 Msun/yr). We conduct counts-in-cells analysis with the multifield ALMA data for the faint SMGs, and obtain a coarse estimate of galaxy bias, b_g <4. The galaxy bias suggests that the dark halo masses of the faint SMGs are <~ 7x10^12 Msun, which is smaller than those of bright (>1 mJy) SMGs, but consistent with abundant high-z star-forming populations such as sBzKs, LBGs, and LAEs. Finally, we report the serendipitous detection of SLE-1 with continuum counterparts neither in our 1.2 mm-band nor multi-wavelength images including ultra deep HST/WFC3 and Spitzer data. The SLE has a significant line at 249.9 GHz with a signal-to-noise ratio of 7.1. If the SLE is not a spurious source made by unknown systematic noise of ALMA, the strong upper limits of our multi-wavelength data suggest that the SLE would be a faint galaxy at z >~ 6.
Constraining dust formation in high-redshift young galaxies
Hiroyuki Hirashita,Andrea Ferrara,Pratika Dayal,Masami Ouchi
Physics , 2014, DOI: 10.1093/mnras/stu1290
Abstract: Core-collapse supernovae (SNe) are believed to be the first significant source of dust in the Universe. Such SNe are expected to be the main dust producers in young high-redshift Lyman $\alpha$ emitters (LAEs) given their young ages, providing an excellent testbed of SN dust formation models during the early stages of galaxy evolution. We focus on the dust enrichment of a specific, luminous LAE (Himiko, $z\simeq 6.6$) for which a stringent upper limit of $52.1~\mu$Jy ($3\sigma$) has recently been obtained from ALMA continuum observations at 1.2 mm. We predict its submillimetre dust emission using detailed models that follow SN dust enrichment and destruction and the equilibrium dust temperature, and obtain a plausible upper limit to the dust mass produced by a single SN: $m_\mathrm{d,SN} < 0.15$--0.45 M$_\odot$, depending on the adopted dust optical properties. These upper limits are smaller than the dust mass deduced for SN 1987A and that predicted by dust condensation theories, implying that dust produced in SNe are likely to be subject to reverse shock destruction before being injected into the interstellar medium. Finally, we provide a recipe for deriving $m_\mathrm{d,SN}$ from submillimetre observations of young, metal poor objects wherein condensation in SN ejecta is the dominant dust formation channel.
First Infrared-based implications for the dust attenuation and star formation of typical Ly$α$ emitters
Haruka Kusakabe,Kazuhiro Shimasaku,Kimihiko Nakajima,Masami Ouchi
Physics , 2014, DOI: 10.1088/2041-8205/800/2/L29
Abstract: By stacking publicly available deep Spitzer/MIPS 24 $\mu$m and Herschel/PACS images for 213 $z \simeq 2.18$ Ly$\alpha$ Emitters (LAEs) in GOODS-South, we obtain a strong upper limit to the IR luminosity of typical LAEs and discuss their attenuation curve for the first time. The $3\sigma$ upper limit $L_{\rm TIR}^{3\sigma}= 1.1 \times 10^{10} L_\odot$, determined from the MIPS data providing the lowest limit, gives $IRX \equiv L_{\rm TIR}/L_{\rm UV} \leq 2.2$. Here we assume that the local calibration between the 8 $\mu$m emission and the dust SED shape and metallicity applies at high redshifts and that our LAEs have low metallicities as suggested by previous studies. The inferred escape fractions of Ly$\alpha$, $16$--$37%$, and UV continuum, $\ge 44%$, are higher than the cosmic averages at the same epoch. The SMC attenuation curve is consistent with the IRX and the UV slope $\beta = -1.4^{+0.2}_{-0.2}$ of our stacked LAE, while the Meurer's relation (Calzetti curve) predicts a 3.8 times higher IRX; we also discuss the validity of PACS-based $L_{\rm TIR}^{3\sigma}$ allowing the Meurer's relation. SED fitting using the Calzetti curve also gives a $\sim 10$ times higher SFR than from the $L_{\rm TIR}^{3\sigma}$ and $L_{\rm UV}$. With $M_{\star}=6.3^{+0.8}_{-2.0} \times10^8 \mathrm{M_{\odot}}$, our LAEs lie on a lower-mass extrapolation of the star formation main sequence at $z \sim 2$, suggesting that the majority of $z \sim 2$ LAEs are mildly star forming with relatively old ages of $\sim 200$ Myr. The faint $L_{\rm TIR}^{3\sigma}$ implies that LAEs contribute little to the faint ($\gtrsim 100 \mu$Jy) submm number counts by ALMA.
Expected Sub-mm Emission and Dust Properties of Lyman Break Galaxies at High Redshift
Masami Ouchi,Toru Yamada,Hideaki Kawai,Kouji Ohta
Physics , 1999, DOI: 10.1086/312021
Abstract: We investigate expected sub-mm emission and dust properties of the Lyman Break Galaxies (LBGs) in the Hubble Deep Field (HDF). The SCUBA Deep Survey (Hughes et al., 1998) provides an upper limit of the 850 micron flux densities of the LBGs. With this constraint, we argue that a typical ultra-violet to far-infrared spectral shape of the high-redshift LBGs is rather close to a template spectrum of low-reddening starburst galaxies in the local universe but different from that of heavily dust-enshrouded ultra-luminous far-infrared galaxies like Arp220. We also evaluate the lower-limit temperature of dust in LBGs assuming single- and two-component modified black-body spectrum. To estimate the total amount of energy re-emitted in FIR wavelength, we take two different approaches; model fitting of the UV spectra of LBGs and an empirical method using the relationship between UV spectral shape and UV/FIR flux ratio observed for local starburst galaxies. Both methods give lower-limit temperature of the LBGs as around 40 K, which is higher than the typical dust temperature of local optical- and infrared-selected galaxies. This result is also supported by the comparison of the expected sub-mm flux of the LBGs with the cosmic FIR background radiation. The high dust temperature may indicate the effective massive-star formation or different dust properties in the high-redshift LBGs.
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