arXiv subjects

Keiichi Kodaira

Publications and source records attributed to Keiichi Kodaira.

7 recordsLinked to original sources

arXiv2026

Scaling Relations across Galaxy Classification Schemes: I. Star Formation Rate-Stellar Mass Plane of CALIFA Nearby Galaxies

To gain deeper insights into galaxy evolution and the mechanisms driving transitions between different galaxy morphologies, we analyse the connection between star formation rate and stellar mass for 231 galaxies spanning Hubble types E1-Sdm from the Calar Alto Legacy Integral Field Spectroscopy Area survey using three complementary classification schemes. The Hubble classification provides structural information, the circular velocity curve classification$-$based on principal component analysis$-$ traces the total gravitational potential, and the Quenching classification$-$derived from H$_α$ equivalent width maps$-$indicates the spatial extent of quenched regions relative to star-forming areas. We find a clear separation of galaxy populations on the star formation rate-stellar mass plane. Late-type spirals with slow-rising circular velocity curves, represented by star-forming and quiescent-nuclear-ring galaxies, dominate the blue cloud. Early-type spirals with flat or round-peaked circular velocity curves belonging to centrally quiescent or mixed class populate the green valley, representing a transitional stage. Elliptical and lenticular galaxies with round- or sharp-peaked circular velocity curves from nearly retired or fully retired QSs reside on the red sequence. Furthermore, our results indicate that the morphological groups Sc-Scd, Sd-Sdm, and E1-E3 are characterized by a unique set of QSs and circular velocity curves, while galaxies with morphologies such as Sa-Sbc spread over multiple QSs and circular velocity curves. The distribution of the classification classes shows a tight link between galaxy structure, gravitational potential, and suppression of star-formation in the galaxies.

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arXiv2017

Towards a new classification of galaxies: principal component analysis of CALIFA circular velocity curves

We present a galaxy classification system for 238 (E1-Sdm) CALIFA (Calar Alto Legacy Integral Field Area) galaxies based on the shapes and amplitudes of their circular velocity curves (CVCs). We infer the CVCs from the de-projected surface brightness of the galaxies, after scaling by a constant mass-to-light ratio based on stellar dynamics - solving axisymmetric Jeans equations via fitting the second velocity moment $V_{\mathrm{rms}}=\sqrt{V^2+σ^2}$ of the stellar kinematics. We use principal component analysis (PCA) applied to the CVC shapes to find characteristic features and use a $k$-means classifier to separate circular curves into classes. This objective classification method identifies four different classes, which we name slow-rising (SR), flat (FL), round-peaked (RP) and sharp-peaked (SP) circular curves. SR are typical for low-mass, late-type (Sb-Sdm), young, faint, metal-poor and disc-dominated galaxies. SP are typical for high-mass, early-type (E1-E7), old, bright, metal-rich and bulge-dominated galaxies. FL and RP appear presented by galaxies with intermediate mass, age, luminosity, metallicity, bulge-to-disk ratio and morphologies (E4-S0a, Sa-Sbc). The discrepancy mass factor, $f_d=1-M_{*}/M_{dyn}$, have the largest value for SR and SP classes ($\sim$ 74 per cent and $\sim$ 71 per cent, respectively) in contrast to the FL and RP classes (with $\sim$ 59 per cent and $\sim$ 61 per cent, respectively). Circular curve classification presents an alternative to typical morphological classification and appears more tightly linked to galaxy evolution.

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arXiv2004

Current Performance and On-Going Improvements of the 8.2 m Subaru Telescope

An overview of the current status of the 8.2 m Subaru Telescope constructed and operated at Mauna Kea, Hawaii, by the National Astronomical Observatory of Japan is presented. The basic design concept and the verified performance of the telescope system are described. Also given are the status of the instrument package offered to the astronomical community, the status of operation, and some of the future plans. The status of the telescope reported in a number of SPIE papers as of the summer of 2002 are incorporated with some updates included as of 2004 February. However, readers are encouraged to check the most updated status of the telescope through the home page, http://subarutelescope.org/index.html, and/or the direct contact with the observatory staff.

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arXiv2003

Are Two z~6 Quasars Gravitationally Lensed ?

Several high-z (z > 5.7) quasars have been found in the course of Sloan Digital Sky Survey. The presence of such very high-z quasars is expected to give constraints on early structure formation. On one hand, it is suggested that these most luminous objects at high redshift are biased toward the highly magnified objects by gravitational lensing. To clarify the effect of gravitational lensing on the high-z quasars, we began the imaging survey of intervening lensing galaxies. Indeed our previous optical image showed that SDSSp J104433.04+012502.2 at z=5.74 is gravitationally magnified by a factor 2. In this paper, we report our new optical imaging of other two high-z quasars, SDSSp J103027.10+052455.0 at z=6.28 and SDSSp J130608.26+035626.3 at z=5.99. Since we find neither intervening galaxy nor counter image with i^{\prime} < 25.4-25.8 around each quasar, we conclude that they are not strongly magnified regardless that a lens galaxy is dusty.

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arXiv2002

A Search for Lyman alpha Emitters at Redshift 3.7

We present the results of a survey for emission-line objects based on optical intermediate-band ($λ_{\rm c}$ = 5736 Å~ and $Δλ$ = 280 Å) and broad-band ($B$, $V$, $R$, and $i^\prime$) observations of the Subaru/XMM-Newton Deep Field on the 8.2 m Subaru telescope with the Subaru Prime Focus Camera, Suprime-Cam. All the data were obtained during the guaranteed time observations of the Suprime-Cam instrument. The intermediate-band image covered a sky area with 10\minpoint62 $\times 12\minpoint40 \approx 132$ arcmin$^2$ in the Subaru/XMM-Newton Deep Field (Ouchi et al.). Using this image, we have found 23 emission-line sources whose observed emission-line equivalent widths are greater than 250 Å. Their optical multicolor properties indicate that six emission-line sources are Ly$α$ emitters at $z \approx$ 3.7 ($Δz \approx 0.22$). They are either intense starburst galaxies or active galactic nuclei like quasars at $z \approx$ 3.7. Two more emission-line sources may also be Ly$α$ emitters at $z \approx$ 3.7 although their multicolor properties are marginal. Among the remaining 15 emission-line objects, eight objects appear strong emission-line galaxies at lower redshift; e.g., [O {\sc ii}] $λ$3727 emitters at $z \approx 0.54$, H$β$ at $z \approx 0.18$, or [O {\sc iii}]$λ$5007 emitters at $z \approx 0.15$. The remaining seven objects are unclassified because they are too faint to be detected in broad-band images. We discuss observational properties of these strong emission-line sources. In particular, our data allow us to estimate the star formation density at $z \approx 3.7$ for the first time.

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arXiv2000

ASCA Observations of Three Shakhbazyan's Compact Groups of Galaxies

X-ray observations of three Shakhbazyan's Compact Groups of Galaxies, SCGG 202, SCGG 205, and SCGG 223, are presented for the first time. Extended X-ray emission was detected from SCGG 202 and SCGG 223 with 0.5-2 keV luminosity of 1E42 erg/s and 3E42 erg/s (for H_0 = 75 km/s/Mpc), respectively, while no significant emission was detected from SCGG 205 with an upper limit of 0.7E42 erg/s. The X-ray spectra of SCGG 202 and SCGG 223 can be described with thin-thermal plasma emission with temperature about 1 keV. X-ray properties of SCGG 202 and SCGG 223 are in good agreement with those of other known groups of galaxies, proving the physical nature of their grouping.

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arXiv1999

The Stellar Population of the M31 Spiral Arm Around OB Association A24

A study of the stellar population of the M31 spiral arm around OB association A24 was carried out based on the photometric data obtained from deep V and JHK imaging. The luminosity function was obtained for -7 <~ Mbol <~ -3.5 by applying the extinction correction corresponding to Av=1 and the bolometric correction BC(K) as an empirical function of (J-K)o. In comparing the observed color-luminosity diagrams with semitheoretical isochrones modified for the dust-shell effects, we found the young population of t <~ 30 Myr with supergiants of Mbol <~ -5, the bulk of the intermediate-age population of t ~ 0.2 - 2.5 Gyr with bright asymptotic giant branch (AGB) stars of -5 <~ Mbol <~ -4, and old populations of t ~> 3 Gyr with AGB and red giant branch (RGB) stars of Mbol ~> -4. The average star formation rate was estimated to be ~1.8x10^4 M_o/Myr and ~0.7x10^4 M_o/Myr per deprojected disk area of 1 kpc^2 from the number density of B0 V stars around Mv=-4.0 (age ~10 Myr) and the number density of bright AGB stars around Mbol = -4.3 (age ~1 Gyr), respectively. A study of the local variation in the V and the J and H luminosity functions revealed a kind of anticorrelation between the population of the young component and that of the intermediate-age component when subdomains of ~100 pc scales were concerned. This finding suggests that the disk domain around the A24 area experienced a series of star formation episodes alternatively among different subdomains with a timescale of a few spiral passage periods. Brief discussions are given about the interstellar extinction and about the lifetimes of bright AGB stars and the highly red objects (HROs) in the same area.

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