arXiv subjects

Kentaro Motohara

Publications and source records attributed to Kentaro Motohara.

At least 55 records · Page 3Linked to original sources

arXiv2016

J-GEM Follow-Up Observations of The Gravitational Wave Source GW151226

We report the results of optical--infrared follow-up observations of the gravitational wave (GW) event GW151226 detected by the Advanced LIGO in the framework of J-GEM (Japanese collaboration for Gravitational wave ElectroMagnetic follow-up). We performed wide-field optical imaging surveys with Kiso Wide Field Camera (KWFC), Hyper Suprime-Cam (HSC), and MOA-cam3. The KWFC survey started at 2.26 days after the GW event and covered 778 deg$^2$ centered at the high Galactic region of the skymap of GW151226. We started the HSC follow-up observations from 12 days after the event and covered an area of 63.5 deg$^2$ of the highest probability region of the northern sky with the limiting magnitudes of 24.6 and 23.8 for i band and z band, respectively. MOA-cam3 covered 145 deg$^2$ of the skymap with MOA-red filter 2.5 months after the GW alert. Total area covered by the wide-field surveys was 986.5 deg$^2$. The integrated detection probability of all the observed area was $\sim$29%. We also performed galaxy-targeted observations with six optical and near-infrared telescopes from 1.61 days after the event. Total of 238 nearby (<100 Mpc) galaxies were observed with the typical I band limiting magnitude of $\sim$19.5. We detected 13 supernova candidates with the KWFC survey, and 60 extragalactic transients with the HSC survey. Two third of the HSC transients were likely supernovae and the remaining one third were possible active galactic nuclei. With our observational campaign, we found no transients that are likely to be associated with GW151226.

astro-ph.HE↗

arXiv2016

Merger-induced Shocks in the Nearby LIRG VV 114 through Methanol Observations with ALMA

We report the detection of two CH$_3$OH lines (J$_K$ = 2$_K$-1$_K$ and 3$_K$-2$_K$) between the progenitor's disks ("Overlap") of the mid-stage merging galaxy VV 114 obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 and Band 4. The detected CH$_3$OH emission show an extended filamentary structure (~ 3 kpc) across the progenitor's disks with relatively large velocity width (FWZI ~ 150 km/s). The emission is only significant in the "overlap" and not detected in the two merging nuclei. Assuming optically-thin emission and local thermodynamic equilibrium (LTE), we found the CH$_3$OH column density relative to H$_2$ ($X_{\rm CH_3OH}$) peaks at the "Overlap" (~ 8 $\times$ 10$^{-9}$), which is almost an order of magnitude larger than that at the eastern nucleus. We suggest that kpc-scale shocks driven by galaxy-galaxy collision may play an important role to enhance the CH$_3$OH abundance at the "Overlap". This scenario is consistent with that shock-induced large velocity dispersion components of ionized gas have been detected in optical wavelength at the same region. Conversely, low $X_{\rm CH_3OH}$ at the nuclear regions might be attributed to the strong photodissociation by nuclear starbursts and/or putative active galactic nucleus (AGN), or inefficient production of CH$_3$OH on dust grains due to initial high temperature conditions (i.e., desorption of the precursor molecule, CO, into gas-phase before forming CH$_3$OH on dust grains). These ALMA observations demonstrate that CH$_3$OH is a unique tool to address kpc-scale shock-induced gas dynamics and star formation in merging galaxies.

astro-ph.GA↗

arXiv2016

SXDF-ALMA 2-arcmin^2 Deep Survey: Stacking of Rest-Frame Near-Infrared Selected Objects

We present stacking analyses on our ALMA deep 1.1 mm imaging in the SXDF using 1.6 μm and 3.6 μm selected galaxies in the CANDELS WFC3 catalog. We detect a stacked flux of ~0.03-0.05 mJy, corresponding to LIR < 10^11 Lsun and a star formation rate (SFR) of ~ 15 Msun/yr at z = 2. We find that galaxies brighter in the rest-frame near-infrared tend to be also brighter at 1.1 mm, and galaxies fainter than m[3.6um] = 23 do not produce detectable 1.1 mm emission. This suggests a correlation between stellar mass and SFR, but outliers to this correlation are also observed, suggesting strongly boosted star formation or extremely large extinction. We also find tendencies that redder galaxies and galaxies at higher redshifts are brighter at 1.1 mm. Our field contains z ~ 2.5 H-alpha emitters and a bright single-dish source. However, we do not find evidence of bias in our results caused by the bright source. By combining the fluxes of sources detected by ALMA and fluxes of faint sources detected with stacking, we recover a 1.1 mm surface brightness of up to 20.3 +/- 1.2 Jy/deg, comparable to the extragalactic background light measured by COBE. Based on the fractions of optically faint sources in our and previous ALMA studies and the COBE measurements, we find that approximately half of the cosmic star formation may be obscured by dust and missed by deep optical surveys, Much deeper and wider ALMA imaging is therefore needed to better constrain the obscured cosmic star formation history.

astro-ph.GA↗

arXiv2016

J-GEM Follow-Up Observations to Search for an Optical Counterpart of The First Gravitational Wave Source GW150914

We present our optical follow-up observations to search for an electromagnetic counterpart of the first gravitational wave source GW150914 in the framework of the Japanese collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM), which is an observing group utilizing optical and radio telescopes in Japan, as well as those in New Zealand, China, South Africa, Chile, and Hawaii. We carried out a wide-field imaging survey with Kiso Wide Field Camera (KWFC) on the 1.05-m Kiso Schmidt telescope in Japan and a galaxy-targeted survey with Tripole5 on the B&C 61-cm telescope in New Zealand. Approximately 24 deg2 regions in total were surveyed in i-band with KWFC and 18 nearby galaxies were observed with Tripole5 in g-, r-, and i-bands 4-12 days after the gravitational wave detection. Median 5-sigma depths are i~18.9 mag for the KWFC data and g~18.9 mag, r~18.7 mag, and i~18.3 mag for the Tripole5 data. Probability for a counterpart to be in the observed area is 1.2% in the initial skymap and 0.1% in the final skymap. We do not find any transient source associated to an external galaxy with spatial offset from its center, which is consistent with the local supernova rate. We summarize future prospects and ongoing efforts to pin down electromagnetic counterparts of binary black hole mergers as well as neutron star mergers.

astro-ph.SR↗

arXiv2016

SXDF-ALMA 2 arcmin$^2$ Deep Survey: 1.1-mm Number Counts

We report 1.1 mm number counts revealed with the Atacama Large Millimeter/submillimeter Array (ALMA) in the Subaru/XMM-Newton Deep Survey Field (SXDF). The advent of ALMA enables us to reveal millimeter-wavelength number counts down to the faint end without source confusion. However, previous studies are based on the ensemble of serendipitously-detected sources in fields originally targeting different sources and could be biased due to the clustering of sources around the targets. We derive number counts in the flux range of 0.2-2 mJy by using 23 (>=4sigma) sources detected in a continuous 2.0 arcmin$^2$ area of the SXDF. The number counts are consistent with previous results within errors, suggesting that the counts derived from serendipitously-detected sources are not significantly biased, although there could be field-to-field variation due to the small survey area. By using the best-fit function of the number counts, we find that ~40% of the extragalactic background light at 1.1 mm is resolved at S(1.1mm) > 0.2 mJy.

astro-ph.GA↗

arXiv2015

Spatially-resolved Radio-to-Far-infrared SED of the Luminous Merger Remnant NGC 1614 with ALMA and VLA

We present the results of Atacama Large Millimeter/Submillimeter Array (ALMA) 108, 233, 352, and 691 GHz continuum observations and Very Large Array (VLA) 4.81 and 8.36 GHz observations of the nearby luminous merger remnant NGC 1614. By analyzing the beam (1".0 * 1".0) and uv (> 45 kλ) matched ALMA and VLA maps, we find that the deconvolved source size of lower frequency emission (< 108 GHz) is more compact (420 pc * 380 pc) compared to the higher frequency emission (> 233 GHz) (560 pc * 390 pc), suggesting different physical origins for the continuum emission. Based on an SED model for a dusty starburst galaxy, it is found that the SED can be explained by three components, (1) non-thermal synchrotron emission (traced in the 4.81 and 8.36 GHz continuum), (2) thermal free-free emission (traced in the 108 GHz continuum), and (3) thermal dust emission (traced in the 352 and 691 GHz continuum). We also present the spatially-resolved (sub-kpc scale) Kennicutt-Schmidt relation of NGC 1614. The result suggests a systematically shorter molecular gas depletion time in NGC 1614 (average τ_gas of 49 - 77 Myr and 70 - 226 Myr at the starburst ring and the outer region, respectively) than that of normal disk galaxies (~ 2 Gyr) and a mid-stage merger VV 114 (= 0.1 - 1 Gyr). This implies that the star formation activities in U/LIRGs are efficiently enhanced as the merger stage proceeds, which is consistent with the results from high-resolution numerical merger simulations.

astro-ph.GA↗

arXiv2015

Compact starbursts in z~3-6 submillimeter galaxies revealed by ALMA

We report the source size distribution, as measured by ALMA millimetric continuum imaging, of a sample of 13 AzTEC-selected submillimeter galaxies (SMGs) at z_photo ~ 3-6. Their infrared luminosities and star-formation rates (SFR) are L_IR ~ 2-6 x 10^12 L_sun and ~ 200-600 M_sun yr-1, respectively. The size of z ~ 3-6 SMGs ranges from 0".10 to 0".38 with a median of 0".20+0".03-0".05 (FWHM), corresponding to a median circularized effective radius (Rc,e) of 0.67+0.13-0.14 kpc, comparable to the typical size of the stellar component measured in compact quiescent galaxies at z ~ 2 (cQGs) --- R ~ 1 kpc. The median surface SFR density of our z ~ 3-6 SMGs is 100+42-26 M_sun yr-1 kpc-2, comparable to that seen in local merger-driven (U)LIRGsrather than in extended disk galaxies at low and high redshifts. The discovery of compact starbursts in z >~ 3 SMGs strongly supports a massive galaxy formation scenario wherein z ~ 3-6 SMGs evolve into the compact stellar components of z ~ 2 cQGs. These cQGs are then thought to evolve into the most massive ellipticals in the local Universe, mostly via dry mergers. Our results thus suggest that z >~ 3 SMGs are the likely progenitors of massive local ellipticals, via cQGs, meaning that we can now trace the evolutionary path of the most massive galaxies over a period encompassing ~ 90% of the age of the Universe.

astro-ph.GA↗

arXiv2015

Constraining the Amount of Circumstellar Matter and Dust around Type Ia Supernovae through Near-Infrared Echoes

The circumstellar (CS) environment is key to understanding progenitors of type Ia supernovae (SNe Ia), as well as the origin of a peculiar extinction property toward SNe Ia for cosmological application. It has been suggested that multiple scatterings of SN photons by CS dust may explain the non-standard reddening law. In this paper, we examine the effect of re-emission of SN photons by CS dust in the infrared (IR) wavelength regime. This effect allows the observed IR light curves to be used as a constraint on the position/size and the amount of CS dust. The method was applied to observed near-infrared (NIR) SN Ia samples; meaningful upper limits on the CS dust mass were derived even under conservative assumptions. We thereby clarify a difficulty associated with the CS dust scattering model as a general explanation for the peculiar reddening law, while it may still apply to a sub-sample of highly reddened SNe Ia. For SNe Ia in general, the environment at the interstellar scale appears to be responsible for the non-standard extinction law. Furthermore, deeper limits can be obtained using the standard nature of SN Ia NIR light curves. In this application, an upper limit of Mdot ~10^{-8}-10^{-7} Msun/yr (for the wind velocity of ~10 km/s) is obtained for a mass loss rate from a progenitor up to ~0.01 pc, and Mdot ~10^{-7}-10^{-6} Msun/yr up to ~0.1 pc.

astro-ph.SR↗

arXiv2015

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

We present results from Subaru/FMOS near-infrared (NIR) spectroscopy of 118 star-forming galaxies at $z\sim1.5$ in the Subaru Deep Field. These galaxies are selected as [OII]$λ$3727 emitters at $z\approx$ 1.47 and 1.62 from narrow-band imaging. We detect H$α$ emission line in 115 galaxies, [OIII]$λ$5007 emission line in 45 galaxies, and H$β$, [NII]$λ$6584, and [SII]$λλ$6716,6731 in 13, 16, and 6 galaxies, respectively. Including the [OII] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate physical conditions of the interstellar medium in star-forming galaxies at $z\sim$1.5. We find a tight correlation between H$α$ and [OII], which suggests that [OII] can be a good star formation rate (SFR) indicator for galaxies at $z\sim1.5$. The line ratios of H$α$/[OII] are consistent with those of local galaxies. We also find that [OII] emitters have strong [OIII] emission lines. The [OIII]/[OII] ratios are larger than normal star-forming galaxies in the local Universe, suggesting a higher ionization parameter. Less massive galaxies have larger [OIII]/[OII] 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.

astro-ph.GA↗

arXiv2015

ANIR : Atacama Near-Infrared Camera for the 1.0-m miniTAO Telescope

We have developed a near-infrared camera called ANIR (Atacama Near-InfraRed camera) for the University of Tokyo Atacama Observatory 1.0m telescope (miniTAO) installed at the summit of Cerro Chajnantor (5640 m above sea level) in northern Chile. The camera provides a field of view of 5'.1 $\times$ 5'.1 with a spatial resolution of 0".298 /pixel in the wavelength range of 0.95 to 2.4 $μ$m. Taking advantage of the dry site, the camera is capable of hydrogen Paschen-$α$ (Pa$α$, $λ=$1.8751 $μ$m in air) narrow-band imaging observations, at which wavelength ground-based observations have been quite difficult due to deep atmospheric absorption mainly from water vapor. We have been successfully obtaining Pa$α$ images of Galactic objects and nearby galaxies since the first-light observation in 2009 with ANIR. The throughputs at the narrow-band filters ($N1875$, $N191$) including the atmospheric absorption show larger dispersion (~10%) than those at broad-band filters (a few %), indicating that they are affected by temporal fluctuations in Precipitable Water Vapor (PWV) above the site. We evaluate the PWV content via the atmospheric transmittance at the narrow-band filters, and derive that the median and the dispersion of the distribution of the PWV are 0.40+/-0.30 mm for $N1875$ and 0.37+/-0.21 mm for $N191$, which are remarkably smaller (49+/-38% for $N1875$ and 59+/-26% for $N191$) than radiometry measurements at the base of Cerro Chajnantor (5100 m alt.). The decrease in PWV can be explained by the altitude of the site when we assume that the vertical distribution of the water vapor is approximated at an exponential profile with scale heights within 0.3-1.9 km (previously observed values at night). We thus conclude that miniTAO/ANIR at the summit of Cerro Chajnantor indeed provides us an excellent capability for a "ground-based" Pa$α$ observation.

astro-ph.IM↗

arXiv2015

ALMA Multi-line Observations of the IR-bright Merger VV 114

We present ALMA cycle 0 observations of the molecular gas and dust in the IR-bright mid-stage merger VV114 obtained at 160 - 800 pc resolution. The main aim of this study is to investigate the distribution and kinematics of the cold/warm gas and to quantify the spatial variation of the excitation conditions across the two merging disks. The data contain 10 molecular lines, including the first detection of extranuclear CH3OH emission in interacting galaxies, as well as continuum emission. We map the 12CO(3-2)/12CO(1-0) and the 12CO(1-0)/13CO(1-0) line ratio at 800 pc resolution (in the units of K km/s), and find that these ratios vary from 0.2 - 0.8 and 5 - 50, respectively. Conversely, the 200 pc resolution HCN(4-3)/HCO+(4-3) line ratio shows low values (< 0.5) at a filament across the disks except for the unresolved eastern nucleus which is three times higher (1.34 +/- 0.09). We conclude from our observations and a radiative transfer analysis that the molecular gas in the VV114 system consists of five components with different physical and chemical conditions; i.e., 1) dust-enshrouded nuclear starbursts and/or AGN, 2) wide-spread star forming dense gas, 3) merger-induced shocked gas, 4) quiescent tenuous gas arms without star formation, 5) H2 gas mass of (3.8 +/- 0.7) * 10^7 Msun (assuming a conversion factor of α_CO = 0.8 Msun (K km s^-1 pc^2)^-1) at the tip of the southern tidal arm, as a potential site of tidal dwarf galaxy formation.

astro-ph.GA↗

arXiv2015

Multi-wavelength observations of the black widow pulsar 2FGL J2339.6-0532 with OISTER and Suzaku

Multi-wavelength observations of the black-widow binary system 2FGL J2339.6-0532 are reported. The Fermi gamma-ray source 2FGL J2339.6-0532 was recently categorized as a black widow in which a recycled millisecond pulsar (MSP) is evaporating up the companion star with its powerful pulsar wind. Our optical observations show clear sinusoidal light curves due to the asymmetric temperature distribution of the companion star. Assuming a simple geometry, we constrained the range of the inclination angle of the binary system to 52$^{\circ}$ < i < 59$^{\circ}$, which enables us to discuss the interaction between the pulsar wind and the companion in detail. The X-ray spectrum consists of two components: a soft, steady component that seems to originate from the surface of the MSP, and a hard variable component from the wind-termination shock near the companion star. The measured X-ray luminosity is comparable to the bolometric luminosity of the companion, meaning that the heating efficiency is less than 0.5. In the companion orbit, 10$^{11}$ cm from the pulsar, the pulsar wind is already in particle dominant-stage, with a magnetization parameter of $σ$ < 0.1. In addition, we precisely investigated the time variations of the X-ray periodograms and detected a weakening of orbital modulation. The observed phenomenon may be related to an unstable pulsar-wind activity or a weak mass accretion, both of which can result in the temporal extinction of radio-pulse.

astro-ph.HE↗

arXiv2014

Ground-based Pa$α$ Narrow-band Imaging of Local Luminous Infrared Galaxies I: Star Formation Rates and Surface Densities

Luminous infrared galaxies (LIRGs) are enshrouded by a large amount of dust, produced by their active star formation, and it is difficult to measure their activity in the optical wavelength. We have carried out Pa$α$ narrow-band imaging observations of 38 nearby star-forming galaxies including 33 LIRGs listed in $IRAS$ RBGS catalog with the Atacama Near InfraRed camera (ANIR) on the University of Tokyo Atacama Observatory (TAO) 1.0 m telescope (miniTAO). Star formation rates (SFRs) estimated from the Pa$α$ fluxes, corrected for dust extinction using the Balmer Decrement Method (typically $A_V$ $\sim$ 4.3 mag), show a good correlation with those from the bolometric infrared luminosity of $IRAS$ data within a scatter of 0.27 dex. This suggests that the correction of dust extinction for Pa$α$ flux is sufficient in our sample. We measure the physical sizes and the surface density of infrared luminosities ($Σ_{L(\mathrm{IR})}$) and $SFR$ ($Σ_{SFR}$) of star-forming region for individual galaxies, and find that most of the galaxies follow a sequence of local ultra luminous or luminous infrared galaxies (U/LIRGs) on the $L(\mathrm{IR})$-$Σ_{L(\mathrm{IR})}$ and $SFR$-$Σ_{SFR}$ plane. We confirm that a transition of the sequence from normal galaxies to U/LIRGs is seen at $L(\mathrm{IR})=8\times10^{10}$ $L_{\odot}$. Also, we find that there is a large scatter in physical size, different from those of normal galaxies or ULIRGs. Considering the fact that most of U/LIRGs are merging or interacting galaxies, this scatter may be caused by strong external factors or differences of their merging stage.

astro-ph.GA↗

arXiv2014

High-z gamma-ray bursts for unraveling the dark ages mission HiZ-GUNDAM

We are now investigating and studying a small satellite mission HiZ-GUNDAM for future observation of gamma-ray bursts (GRBs). The mission concept is to probe "the end of dark ages and the dawn of formation of astronomical objects", i.e. the physical condition of early universe beyond the redshift z > 7. We will consider two kinds of mission payloads, (1) wide field X-ray imaging detectors for GRB discovery, and (2) a near infrared telescope with 30 cm in diameter to select the high-z GRB candidates effectively. In this paper, we explain some requirements to promote the GRB cosmology based on the past observations, and also introduce the mission concept of HiZ-GUNDAM and basic development of X-ray imaging detectors.

astro-ph.IM↗

arXiv2013

The Arches cluster out to its tidal radius: dynamical mass segregation and the effect of the extinction law on the stellar mass function

The Galactic center is the most active site of star formation in the Milky Way Galaxy, where particularly high-mass stars have formed very recently and are still forming today. However, since we are looking at the Galactic center through the Galactic disk, knowledge of extinction is crucial when studying this region. The Arches cluster is a young, massive starburst cluster near the Galactic center. We observed the Arches cluster out to its tidal radius using Ks-band imaging obtained with NAOS/CONICA at the VLT combined with Subaro/Cisco J-band data to gain a full understanding of the cluster mass distribution. We show that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, we show that the difference can reach up to 30% for individually derived stellar masses and Delta AKs ~ 1 magnitude in acquired Ks-band extinction, while the present-day mass function slope changes by ~ 0.17 dex. The present-day mass function slope derived assuming the more recent extinction law increases from a flat slope of alpha_{Nishi}=-1.50 \pm0.35 in the core (r<0.2 pc) to alpha_{Nishi}=-2.21 \pm0.27 in the intermediate annulus (0.2 <r<0.4 pc), where the Salpeter slope is -2.3. The mass function steepens to alpha_{Nishi}=-3.21 \pm0.30 in the outer annulus (0.4<r<1.5 pc), indicating that the outer cluster region is depleted of high-mass stars. This picture is consistent with mass segregation owing to the dynamical evolution of the cluster.

astro-ph.SR↗

arXiv2012

Unusual Long and Luminous Optical Transient in the Subaru Deep Field

We present observations of SDF-05M05, an unusual optical transient discovered in the Subaru Deep Field (SDF). The duration of the transient is > ~800 d in the observer frame, and the maximum brightness during observation reached approximately 23 mag in the i' and z' bands. The faint host galaxy is clearly identified in all 5 optical bands of the deep SDF images. The photometric redshift of the host yields z~0.6 and the corresponding absolute magnitude at maximum is ~-20. This implies that this event shone with an absolute magnitude brighter than -19 mag for approximately 300 d in the rest frame, which is significantly longer than a typical supernova and ultra-luminous supernova. The total radiated energy during our observation was 1x10^51 erg. The light curves and color evolution are marginally consistent with some of luminous IIn supernova. We suggest that the transient may be a unique and peculiar supernova at intermediate redshift.

astro-ph.CO↗

arXiv2012

Discovery of a protocluster at z~6

We report the discovery of a protocluster at z~6 containing at least eight cluster member galaxies with spectroscopic confirmations in the wide-field image of the Subaru Deep Field (SDF). The overdensity of the protocluster is significant at the 6 sigma level, based on the surface number density of i'-dropout galaxies. The overdense region covers ~36 sq. arcmin, and includes 30 i'-dropout galaxies. Follow-up spectroscopy revealed that 15 of these are real z~6 galaxies (5.7 < z < 6.3). Eight of the 15 are clustering in a narrow redshift range centered at z=6.01, corresponding to a seven-fold increase in number density over the average in redshift space. We found no significant difference in the observed properties, such as Ly-alpha luminosities and UV continuum magnitudes, between the eight protocluster members and the seven non-members. The velocity dispersion of the eight protocluster members is 647 km/s, which is about three times higher than that predicted by the standard cold dark matter model. This discrepancy could be attributed to the distinguishing three-dimensional distribution of the eight protocluster members. We discuss two possible explanations for this discrepancy: either the protocluster is already mature, with old galaxies at the center, or it is still immature and composed of three subgroups merging to become a larger cluster. In either case, this concentration of z=6.01 galaxies in the SDF may be one of the first sites of formation of a galaxy cluster in the universe.

astro-ph.CO↗

arXiv2011

A Census of Star-Forming Galaxies at z = 1-3 in the Subaru Deep Field

Several UV and near-infrared color selection methods have identified galaxies at z = 1-3. Since each method suffers from selection biases, we have applied three leading techniques (Lyman break, BX/BM, and BzK selection) simultaneously in the Subaru Deep Field. This field has reliable (Δz/(1 + z) = 0.02--0.09) photometric redshifts for ~53,000 galaxies from 20 bands (1500Å--2.2μm). The BzK, LBG, and BX/BM samples suffer contamination from z<1 interlopers of 6%, 8%, and 20%, respectively. Around the redshifts where it is most sensitive (z~1.9 for star-forming BzK, z~1.8 for z~2 LBGs, z~1.6 for BM, and z~2.3 for BX), each technique finds 60-80% of the census of the three methods. In addition, each of the color techniques shares 75-96% of its galaxies with another method, which is consistent with previous studies that adopt identical criteria on magnitudes and colors. Combining the three samples gives a comprehensive census that includes ~90% of z-phot = 1-3 galaxies, using standard magnitude limits similar to previous studies. In fact, we find that among z = 1-2.5 galaxies in the color selection census, 81-90% of them can be selected by just combining the BzK selection with one of the UV techniques (z~2 LBG or BX and BM). The average galaxy stellar mass, reddening and SFRs all decrease systematically from the sBzK population to the LBGs, and to the BX/BMs. The combined color selections yield a total cosmic SFR density of 0.18 $\pm$ 0.03 M_sun yr^{-1} Mpc^{-3} for K_AB <= 24. We find that 65% of the star formation is in galaxies with E(B-V) > 0.25 mag, even though they are only one-fourth of the census by number.

astro-ph.CO↗