arXiv subjects

M. Hamabe

Publications and source records attributed to M. Hamabe.

15 recordsLinked to original sources

arXiv2007

The Galaxy Luminosity Functions down to M~-10 in the Hydra I Cluster

We study the galaxy population in the central region and a region about 0.6 Mpc away from the center of the Hydra I cluster in B- and Rc-bands down to M~-10 using the Subaru Suprime-Cam photometry. We find that the luminosity function of the entire population has a slightly steeper slope (alpha~-1.6) in the range of -20 -14) increases in the cluster center as well as bright galaxies. The Hydra I cluster is dominated by red dwarfs and the luminosity function shows a significant upturn at M~-16 as is seen in several other nearby clusters, but not in the field. This upturn and the variation in the faint-end slope of the luminosity function may be caused by the cluster environment or the evolution history of individual clusters.

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arXiv2004

Subaru Deep Survey VI. A Census of Lyman Break Galaxies at z=4 and 5 in the Subaru Deep Fields: Clustering Properties

We investigate the clustering properties of 2,600 Lyman Break Galaxies (LBGs) at z=3.5-5.2 in two large blank fields, the Subaru Deep Field and the Subaru/XMM Deep Field (600arcmin^2 each). The angular correlation functions of these LBGs show a clear clustering at both z~4 and 5. The correlation lengths are r_0= 4.1^{+0.2}_{-0.2} and 5.9^{+1.3}_{-1.7} h_{100}^{-1} Mpc (r_0= 5.1^{+1.0}_{-1.1} and 5.9^{+1.3}_{-1.7} h_{100}^{-1} Mpc) for all the detected LBGs (for L>L* LBGs) at z~4 and 5, respectively. These correlation lengths correspond to galaxy-dark matter biases of b_g= 2.9^{+0.1}_{-0.1} and 4.6^{+0.9}_{-1.2} (b_g=3.5^{+0.6}_{-0.7} and 4.6^{+0.9}_{-1.2}), for all the detected LBGs (for L>L^* LBGs) at z~4 and 5, respectively. These results, combined with estimates for z~3 LBGs in the literature, show that the correlation length of L>L^* LBGs is almost constant, ~5 h_{100}^{-1} Mpc, over z~3-5, while the bias monotonically increases with redshift at z>3. We also find that for LBGs at z~4 the clustering amplitude increases with UV-continuum luminosity and with the amount of dust extinction. We estimate the mass of dark halos hosting various kinds of high-z galaxies including LBGs with the analytic model given by Sheth & Tormen (1999). We find that the typical mass of dark halos hosting L>L^* LBGs is about 1x10^{12} h_{70}^{-1}Msol over z~3-5, which is comparable to that of the Milky Way Galaxy. A single dark halo with ~10^{12} h_{70}^{-1} Msol is found to host 0.1-0.3 LBG on average but host about four K-band selected galaxies.

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arXiv2004

Subaru Deep Survey V. A Census of Lyman Break Galaxies at z=4 and 5 in the Subaru Deep Fields: Photometric Properties

(abridged) We investigate photometric properties of Lyman Break Galaxies (LBGs) at z=3.5-5.2 based on large samples of 2,600 LBGs detected in deep (i'~27) and wide-field (1,200 arcmin^2) images taken in the Subaru Deep Field (SDF) and the Subaru/XMM Deep Field (SXDF). The selection criteria for the LBG samples are examined with 85 spectroscopically identified objects and by Monte Carlo simulations. We find in the luminosity functions of LBGs (i) that the number density of bright galaxies (M_{1700}<-22; corresponding to SFR_{corr}>100 Msolar yr^{-1}) decreases significantly from z=4 to 5 and (ii) that the faint-end slope of the luminosity function may become steeper towards higher redshifts. We estimate dust extinction of z=4 LBGs with M ~0.13.

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arXiv2003

Subaru Deep Spectroscopy of the Very Extended Emission-Line Region of NGC 4388: Ram Pressure Stripped Gas Ionized by the Nuclear Radiation

We report here the results of deep optical spectroscopy of the very extended emission-line region (VEELR) found serendipitously around the Seyfert 2 galaxy NGC 4388 in the Virgo cluster using the Subaru Telescope. The H-alpha recession velocities of most of the filaments of the region observed are highly blue-shifted with respect to the systemic velocity of the galaxy. The velocity field is complicated, and from the kinematic and morphological points of view, there seem to be several streams of filaments: low velocity (v = -100 km/s) filaments, high velocity (v = -300 km/s) filaments, and a very high velocity (v > -500 km/s) cloud complex. The emission-line ratios of the VEELR filaments are well explained by power-law photoionization models with solar abundances, suggesting that the Seyfert nucleus of NGC 4388 is the dominant ionization source of the VEELR and that the VEELR gas has moderate metallicity. In addition to photoionization, shock heating probably contributes to the ionization of the gas. In particular, the filaments outside the ionization cone of the Seyfert nucleus are mainly excited by shocks. We conclude that the VEELR was formerly the disk gas of NGC 4388, which has been stripped by ram pressure due to the interaction between the hot intra-cluster medium (ICM) and the galaxy. The velocity field and the morphology of the VEELR closely resemble snapshots from some numerical simulations of this process. In the case of NGC 4388, the ram pressure-stripped gas, which is normally seen as extended HI filaments, happens to be exposed and ionized by the radiation from the AGN, and so can be seen as optical emission-line gas.

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arXiv2003

Cosmic shear statistics in the Suprime-Cam 2.1 sq deg field: Constraints on Omega_m and sigma_8

We present measurements of the cosmic shear correlation in the shapes of galaxies in the Suprime-Cam 2.1 deg^2 R_c-band imaging data. As an estimator of the shear correlation originated from the gravitational lensing, we adopt the aperture mass variance. We detect a non-zero E mode variance on scales between 2 and 40arcmin. We also detect a small but non-zero B mode variance on scales larger than 5arcmin. We compare the measured E mode variance to the model predictions in CDM cosmologies using maximum likelihood analysis. A four-dimensional space is explored, which examines sigma_8, Omega_m, Gamma and zs (a mean redshift of galaxies). We include three possible sources of error: statistical noise, the cosmic variance estimated using numerical experiments, and a residual systematic effect estimated from the B mode variance. We derive joint constraints on two parameters by marginalizing over the two remaining parameters. We obtain an upper limit of Gamma<0.5 for zs>0.9 (68% confidence). For a prior Gamma\in[0.1,0.4] and zs\in[0.6,1.4], we find sigma_8=(0.50_{-0.16}^{+0.35})Omega_m^{-0.37} for flat cosmologies and sigma_8=(0.51_{-0.16}^{+0.29})Omega_m^{-0.34}$ for open cosmologies (95% confidence). If we take the currently popular LCDM model, we obtain a one-dimensional confidence interval on sigma_8 for the 95.4% level, 0.62<σ_8<1.32 for zs\in[0.6,1.4]. Information on the redshift distribution of galaxies is key to obtaining a correct cosmological constraint. An independent constraint on Gamma from other observations is useful to tighten the constraint.

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arXiv2003

Subaru Deep Survey. IV. Discovery of a Large-Scale Structure at Redshift \simeq 5

We report the discovery of a large-scale structure of Lyman alpha emitters (LAEs) at z=4.86 based on wide-field imaging with the prime-focus camera (Suprime-Cam) on the Subaru telescope. We observed a 25' x 45' area of the Subaru Deep Field in a narrow band (NB, lambdaC=7126 A and FWHM=73 A) together with R and i'. We isolate from these data 43 LAE candidates down to NB=25.5 mag using color criteria. Follow-up spectroscopy of five candidates suggests the contamination by low-z objects to be ~ 20%. We find that the LAE candidates are clustered in an elongated region on the sky of 20 Mpc in width and 50 Mpc in length at z=4.86, which is comparable in size to present-day large-scale structures (we adopt H0=70 km/s/Mpc, Omega0=0.3, lambda0=0.7). This elongated region includes a circular region of 12 Mpc radius of higher surface overdensity (delta=2), which may be the progenitor of a cluster of galaxies. Assuming this circular region to be a sphere with a spatial overdensity of 2, we compare our observation with predictions by Cold Dark Matter models. We find that an Omega0=0.3 flat model with sigma8=0.9 predicts the number of such spheres consistent with the observed number (one sphere in our survey volume) if the bias parameter of LAEs is b \simeq 6. This value suggests that the typical mass of dark haloes hosting LAEs at z \simeq 5 is of the order of 10^12 Msolar. Such a large mass poses an interesting question about the nature of LAEs.

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arXiv2002

Narrow band imaging in [OIII] and Halpha to search for ICPNe in the Virgo cluster

We have identified intracluster planetary nebulae in a Virgo cluster core field by imaging with the Subaru Suprime-Cam through two narrow band filters centered at the redshifted wavelengths of the [OIII] $λ=5007$ Åand the H$α$ $λ= 6563$ Ålines; broad-band images in V and R were acquired to check for emission in the adjacent continuum. Emission line objects in Virgo are then selected from the two-color diagram ([OIII] -- Halpha) vs. ([OIII] -- (V+R)), which is calibrated using PNe in M84 (Jacoby et al. 1990). Using both [OIII] and Halpha allows us to distinguish bona-fide planetary nebulae from high redshift emission-line galaxies at the bright end of the [OIII] luminosity function. Spectroscopic observations of a subsample of these objects were made at the TNG and at the VLT, in a region around M84 and in an intracluster field respectively. The observations confirm the efficiency of the combined [OIII]+H$α$ imaging to identify true PNe. We also obtained the first spectrum of an intracluster PN which shows the [OIII] doublet with S/N > 10 and its Halpha emission. From the results based on the spectroscopic follow-up, we derive a lower limit to the fraction of the Virgo cluster light contributed by the intracluster stars at the surveyed position in the cluster core: it amounts to 10%.

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arXiv2002

Candidates for Intracluster Planetary Nebulae in the Virgo Cluster based on the Suprime-Cam Narrow-Band Imaging in O[III] and Halpha

We have identified 38 candidates of intracluster planetary nebulae (ICPNe) in a $34'\times27'$ field in the core of the Virgo cluster based on the Suprime-Cam imaging through two narrow-band filters centered at the redshifted wavelengths of the [OIII]$λ=5007Å$ and the Halpha λ=6563Ålines. Broad-band images in V and R bands are used to check for any emissions in the adjacent continuum. We describe the method briefly and present the list of intracluster planetary nebulae candidates, together with their finding charts. The ICPN candidates show a highly inhomogeneous distribution, which may suggest an association with the M86-M84 subcluster. Fraction of diffuse intracluster light with respect to total light in galaxies is estimated to be about 10%, leading to an estimate of about 20% for the baryon fraction. Spectroscopic follow up and a wider survey are critical to reveal the nature of intracluster stellar population.

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arXiv2002

Evolution of Elliptical Galaxies at z >~ 1 Revealed from a Large, Multicolor Sample of Extremely Red Objects

We study the evolution of elliptical galaxies at z >~ 1 on the basis of a sample of 247 Extremely Red Objects (EROs) with R-Ks >= 3.35 (AB) and Ks <= 22.1 (AB) constructed from BVRi'z'JHKs multicolor data of a 114 arcmin2 area in the Subaru/XMM Deep Survey Field. By fitting template spectra of old ellipticals (OEs) and young, dusty starbursts (DSs) to the multicolor data, we classify EROs into these two classes and estimate their redshifts. We find that 58% of the EROs in our sample belong to the OE class and that 24% of the OEs are fit by a spectrum having a disk component with the B-band bulge-to-total luminosity ratio of <= 0.9. We compare the observed surface density of OEs with predictions from passive evolution models. We then derive rest-frame B-band luminosity functions (LFs) of OEs in our sample at z=1-1.5 and 1.5-2.5. We find that the LF at z=1-1.5 roughly agrees with the LF of local ellipticals if a dimming of 1.3 mag from z=1.25 to the present epoch is assumed. On the other hand, the amplitude of the LF at z=1.5-2.5 is found to be lower than that of the local LF by a factor of ~ 3 over the whole range of magnitude observed. Taking account of a strong decrease in the number density of morphologically classified early-type galaxies at z >~ 1.5 found by several authors, we conclude that the majority of ellipticals seen at present have not established either a red color or a smooth 1/4-law profile before z ~ 1.5$. (abridged)

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arXiv2002

Searching for dark matter halos in the Suprime-Cam 2 sq deg field

We report the first result of weak gravitational lensing survey on a 2.1 sq deg Rc-band image taken with a wide field camera (Suprime-Cam) on the prime focus of 8.2 m Subaru Telescope. The weak lensing mass reconstruction is applied to the data to search for dark matter halos of cluster scale; M >= 10^14 solar mass. The reconstructed convergence field is divided by 1-sigma noise to obtain the signal-to-noise ratio map (S/N-map) of the detection. Local maxima and minima are searched on the S/N-map and the probability distribution function (PDF) of the peaks are created to compare with model predictions. We found excess over noise PDF created from the randomized realization on both positive and negative sides. Negative peaks imply the presence of voids in the dark matter distribution and this is the first report of the detection. Positive peaks, on the other hand, represent the dark matter halos and the number count of the halos on the 2.1 sq deg image is 4.9 +- 2.3 for S/N > 5 where the Gaussian smoothing radius of the convergence map is 1'. The result is consistent with the prediction assuming the Press-Schechter mass function and the NFW halo profile under the cluster normalized CDM cosmology. Although the present statistics is not enough due to the limited field of view, this work demonstrates that dark matter halo count via weak lensing is a promising way to test the paradigm of structure formation and cosmological model.

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arXiv2002

Subaru Deep Survey II. Luminosity Functions and Clustering Properties of Lya Emitters at z=4.86 in the Subaru Deep Field

We report on early results from deep and wide-field narrow-band imaging on a 543 arcmin^2 area of the Subaru Deep Field. We find 87 Lya emitters (LAEs) at z=4.86(+/-0.03) which are photometrically selected by a combination of two broad bands (R and i') and one narrow band (NB711; 7126A FWHM=73A). We derive the luminosity functions (LFs) of the LAEs at Lya luminosity and at UV-continuum (1700A) luminosity. The LFs show little evolution between z=3.4 and z=4.86 either in Lya or UV-continuum emission. The amplitude of the LAE LF tends to decline at the bright magnitudes more rapidly than that of the LBG LF at similar redshifts. We calculate the angular correlation function of our LAEs up to ~15 arcmin separations. The angular correlation w(theta) is found to increase with decreasing angular separations, showing a clear signal of clustering. It is also found that the distribution of LAEs shows a large density gradient with a scale of >~15 arcmin, which would indicate the existence of a large-scale structure of LAEs on >~20h^(-1) Mpc scales.We fit the observed correlation function by Aw theta^(-0.8) to find Aw=29arcsec^(0.8). The estimated correlation length is r0=3.5(+/-0.3)h^(-1)Mpc in comoving units (Omega_m=0.3 and Omega_Lambda=0.7), which is slightly larger than the value for z~4 LBGs with i'<26. We calculate the angular correlation function for two sub-samples of the 87 LAEs divided by Lya luminosity, UV-continuum luminosity, and Lya equivalent width (EW). The Lya bright sub-sample shows a larger correlation amplitude than the Lya faint sub-sample, while no significant difference is found for the sub-samples divided by UV-continuum luminosity or EW.

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arXiv2002

The u'g'r'i'z' Standard Star Network

We present the 158 standard stars that define the u'g'r'i'z' photometric system. These stars form the basis for the photometric calibration of the Sloan Digital Sky Survey (SDSS). The defining instrument system and filters, the observing process, the reduction techniques, and the software used to create the stellar network are all described. We briefly discuss the history of the star selection process, the derivation of a set of transformation equations for the UBVRcIc system, and plans for future work.

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arXiv2001

Statistical Properties of Bright Galaxies in the SDSS Photometric System

We investigate the photometric properties of 456 bright galaxies using imaging data recorded during the commissioning phase of the Sloan Digital Sky Survey (SDSS). Morphological classification is carried out by correlating results of several human classifiers. Our purpose is to examine the statistical properties of color indices, scale lengths, and concentration indices as functions of morphology for the SDSS photometric system. We find that $u'-g'$, $g'-r'$, and $r'-i'$ colors of SDSS galaxies match well with those expected from the synthetic calculation of spectroscopic energy distribution of template galaxies and with those transformed from $UBVR_CI_C$ color data of nearby galaxies. The agreement is somewhat poor, however, for $i'-z'$ color band with a discrepancy of $0.1-0.2$ mag. With the aid of the relation between surface brightness and radius obtained by Kent (1985), we estimate the averages of the effective radius of early type galaxies and the scale length of exponential disks both to be 2.6 kpc for $L^*$ galaxies. We find that the half light radius of galaxies depends slightly on the color bands, consistent with the expected distribution of star-forming regions for late type galaxies and with the known color gradient for early type galaxies. We also show that the (inverse) concentration index, defined by the ratio of the half light Petrosian radius to the 90% light Petrosian radius, correlates tightly with the morphological type; this index allows us to classify galaxies into early (E/S0) and late (spiral and irregular) types, allowing for a 15-20% contamination from the opposite class compared with eye-classified morphology.

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arXiv2000

Deep-Imaging Observations of a Candidate of an Absorbed QSO at z=0.653, AX J131831+3341

The results of deep-imaging observations of a candidate of an absorbed QSO at z=0.653, AX J131831+3341, are presented. AX J131831+3341 was found during the course of optical follow-up observations of the ASCA Large Sky Survey, and has an X-ray luminosity of 10^{45} erg s^{-1} (2-10keV), which corresponds to those of QSOs. Its optical spectrum shows no significant broad H_beta emission line, suggesting that the object is an absorbed QSO. Deep R and V band images reveal the presence of a point-like nucleus and an asymmetric extended component. The nuclear component has a blue color, and the optical magnitude is much fainter than that expected from the observed X-ray flux for typical type-1 AGNs. These photometric properties and the presence of broad MgII 2800A emission can be explained simultaneously if the observed nuclear light is dominated by scattered nuclear light, though there is a possibility that the nuclear component is a slightly absorbed nucleus if its intrinsic X-ray to optical flux ratio is the largest among X-ray selected AGNs. The size of the extended component, which is thought to be the host galaxy of the QSO, is larger than those of normal disk galaxies at z=0-0.75, and the absolute magnitude is similar to those of the brightest host galaxies of QSOs at redshifts smaller than 0.5. The V-R and R-I colors of the component are consistent with a 1 Gyr-old stellar population model without absorption.

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arXiv1993

Face-on Barred Spiral Structure of Molecular Clouds in M31's Bulge

By image processing and color excess analyses of B, V, R, and I-band CCD images of the central region of M31 taken with the Kiso 105-cm Schmidt telescope, we found a bar of 200 pc length. We also found a more extended ``face-on" spiral feature of dark clouds, which appear t o be connected to this bar and is probably an out-of-plane structure. The \co-line emission was detected from the dark clouds using the Nobeyama 45m telescope, and the virial mass of individual clouds was estimated to be about 10E6 solar masses. The CO intensity-to-virial mass ratio is anomalously small, and so is the color excess-to-mass ratio, which indicates a low temperature and a small amount dust per unit gas mass in the cloud, respectively. This implies that the molecular clouds in the central few hundred pc of M31 are more primeval, suggesting a low star-formation and low dust supply. We propose a possible scenario for the origin of the face-on spiral containing such gas on the basis of a ram-pressure accretion model of stripped gas clouds from the companion galaxies. Key words: Dark clouds -- CO line -- Galaxies; individual (M31) -- Interstellar dust -- Nuclei of galaxies.

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