arXiv subjects

M. Kubo

Publications and source records attributed to M. Kubo.

At least 37 records · Page 2Linked to original sources

arXiv2017

Deep submillimeter and radio observations in the SSA22 field. I. Powering sources and Lyα escape fraction of Lyα blobs

We study the heating mechanisms and Lyα escape fractions of 35 Lyα blobs (LABs) at z = 3.1 in the SSA22 field. Dust continuum sources have been identified in 11 of the 35 LABs, all with star formation rates (SFRs) above 100 Msun/yr. Likely radio counterparts are detected in 9 out of 29 investigated LABs. The detection of submm dust emission is more linked to the physical size of the Lyα emission than to the Lyα luminosities of the LABs. A radio excess in the submm/radio detected LABs is common, hinting at the presence of active galactic nuclei. Most radio sources without X-ray counterparts are located at the centers of the LABs. However, all X-ray counterparts avoid the central regions. This may be explained by absorption due to exceptionally large column densities along the line-of-sight or by LAB morphologies, which are highly orientation dependent. The median Lyα escape fraction is about 3\% among the submm-detected LABs, which is lower than a lower limit of 11\% for the submm-undetected LABs. We suspect that the large difference is due to the high dust attenuation supported by the large SFRs, the dense large-scale environment as well as large uncertainties in the extinction corrections required to apply when interpreting optical data.

astro-ph.GA↗

arXiv2017

Chromospheric polarimetry through multi-line observations of the 850 nm spectral region II: A magnetic flux tube scenario

In this publication we continue the work started in Quintero Noda et al. (2017) examining this time a numerical simulation of a magnetic flux tube concentration. Our goal is to study if the physical phenomena that take place in it, in particular, the magnetic pumping, leaves a specific imprint on the examined spectral lines. We find that the profiles from the interior of the flux tube are periodically dopplershifted following an oscillation pattern that is also reflected in the amplitude of the circular polarization signals. In addition, we analyse the properties of the Stokes profiles at the edges of the flux tube discovering the presence of linear polarization signals for the Ca II lines, although they are weak with an amplitude around 0.5% of the continuum intensity. Finally, we compute the response functions to perturbations in the longitudinal field and we estimate the field strength using the weak field approximation. Our results indicate that the height of formation of the spectral lines changes during the magnetic pumping process which makes the interpretation of the inferred magnetic field strength and its evolution more difficult. These results complement those from previous works demonstrating the capabilities and limitations of the 850 nm spectrum for chromospheric Zeeman polarimetry in a very dynamic and complex atmosphere.

astro-ph.SR↗

arXiv2017

Solar polarimetry through the K I lines at 770 nm

We characterize the K I D1 & D2 lines in order to determine whether they could complement the 850 nm window, containing the Ca II infrared triplet lines and several Zeeman sensitive photospheric lines, that was studied previously. We investigate the effect of partial redistribution on the intensity profiles, their sensitivity to changes in different atmospheric parameters, and the spatial distribution of Zeeman polarization signals employing a realistic magnetohydrodynamic simulation. The results show that these lines form in the upper photosphere at around 500 km and that they are sensitive to the line of sight velocity and magnetic field strength at heights where neither the photospheric lines nor the Ca II infrared lines are. However, at the same time, we found that their sensitivity to the temperature essentially comes from the photosphere. Then, we conclude that the K I lines provide a complement to the lines in the 850 nm window for the determination of atmospheric parameters in the upper photosphere, especially for the line of sight velocity and the magnetic field.

astro-ph.SR↗

arXiv2017

Bimodal morphologies of massive galaxies at the core of a protocluster at z=3.09 and the strong size growth of a brightest cluster galaxy

We present the near-infrared high resolution imaging of an extremely dense group of galaxies at the core of the protocluster at $z=3.09$ in the SSA22 field by using the adaptive optics AO188 and the Infrared Camera and Spectrograph (IRCS) on Subaru Telescope. Wide morphological variety of them suggests their on-going dramatic evolutions. One of the two quiescent galaxies (QGs), the most massive one in the group, is a compact elliptical with an effective radius $r_{e} = 1.37\pm0.75$ kpc. It supports the two-phase formation scenario of giant ellipticals today that a massive compact elliptical is formed at once and evolves in the size and stellar mass by series of mergers. Since this object is a plausible progenitor of a brightest cluster galaxy (BCG) of one of the most massive clusters today, it requires strong size ($\ga10$) and stellar mass ($\sim$ four times by $z=0$) growths. Another QG hosts an AGN(s) and is fitted with a model composed from an nuclear component and Sérsic model. It shows spatially extended [O{\footnotesize III}]$λ$5007 emission line compared to the continuum emission, a plausible evidence of outflows. Massive star forming galaxies (SFGs) in the group are two to three times larger than the field SFGs at similar redshift. Although we obtained the $K$-band image deeper than the previous one, we found no candidate new members. This implies a physical deficiency of low mass galaxies with stellar mass $M_{\star}\la4\times10^{10}~M_{\odot}$ and/or poor detection completeness of them owing to their diffuse morphologies.

astro-ph.GA↗

arXiv2017

Discovery of Scattering Polarization in the Hydrogen Lyman-$α$ Line of the Solar Disk Radiation

There is a thin transition region (TR) in the solar atmosphere where the temperature rises from 10,000 K in the chromosphere to millions of degrees in the corona. Little is known about the mechanisms that dominate this enigmatic region other than the magnetic field plays a key role. The magnetism of the TR can only be detected by polarimetric measurements of a few ultraviolet (UV) spectral lines, the Lyman-$α$ line of neutral hydrogen at 121.6 nm (the strongest line of the solar UV spectrum) being of particular interest given its sensitivity to the Hanle effect (the magnetic-field-induced modification of the scattering line polarization). We report the discovery of linear polarization produced by scattering processes in the Lyman-$α$ line, obtained with the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket experiment. The Stokes profiles observed by CLASP in quiet regions of the solar disk show that the $Q/I$ and $U/I$ linear polarization signals are of the order of 0.1 % in the line core and up to a few percent in the nearby wings, and that both have conspicuous spatial variations with scales of $\sim 10$ arcsec. These observations help constrain theoretical models of the chromosphere-corona TR and extrapolations of the magnetic field from photospheric magnetograms. In fact, the observed spatial variation from disk to limb of polarization at the line core and wings already challenge the predictions from three-dimensional magnetohydrodynamical models of the upper solar chromosphere.

astro-ph.SR↗

arXiv2017

ALMA Deep Field in SSA22: Blindly Detected CO Emitters and [CII] Emitter Candidates

We report the identification of four millimeter line emitting galaxies with the Atacama Large Milli/submillimeter Array (ALMA) in SSA22 Field (ADF22). We analyze the ALMA 1.1 mm survey data, with an effective survey area of 5 arcmin$^2$, a frequency range of 253.1--256.8 and 269.1--272.8 GHz, angular resolution of 0".7 and RMS noise of 0.8 mJy beam$^{-1}$ at 36 km s$^{-1}$ velocity resolution. We detect four line emitter candidates with significance levels above $6 σ$. We identify one of the four sources as a CO(9-8) emitter at $z = 3.1$ in a member of the proto-cluster known in this field. Another line emitter with an optical counterpart is likely a CO(4-3) emitter at $z = 0.7$. The other two sources without any millimeter continuum or optical/near-infrared counterpart are likely to be [CII] emitter candidates at $z = 6.0$ and $6.5$. The equivalent widths of the [CII] candidates are consistent with those of confirmed high-redshift [CII] emitters and candidates, and are a factor of 10 times larger than that of the CO(9-8) emitter detected in this search. The [CII] luminosity of the candidates are $4-7 \times 10^8~\rm L_\odot$. The star formation rates (SFRs) of these sources are estimated to be $10-20~\rm M_{\odot}~yr^{-1}$ if we adopt an empirical [CII] luminosity - SFR relation. One of them has a relatively low-S/N ratio, but shows features characteristic of emission lines. Assuming that at least one of the two candidates is a [CII] emitter, we derive a lower limit of [CII]-based star formation rate density (SFRD) at $z~\sim~6$. The resulting value of $> 10^{-2}$ $\rm M_\odot yr^{-1} Mpc^{-3}$ is consistent with the dust-uncorrected UV-based SFRD. Future millimeter/submillimeter surveys can be used to detect a number of high redshift line emitters, with which to study the star formation history in the early Universe.

astro-ph.GA↗

arXiv2016

A resolved map of the infrared excess in a Lyman Break Galaxy at z=3

We have observed the dust continuum of ten z=3.1 Lyman Break Galaxies with the Atacama Large Millimeter/Submillimeter Array at ~450 mas resolution in Band 7. We detect and resolve the 870um emission in one of the targets with an integrated flux density of S(870)=(192+/-57) uJy, and measure a stacked 3-sigma signal of S(870)=(67+/-23) uJy for the remaining nine. The total infrared luminosities estimated from full spectral energy distribution fits are L(8-1000um)=(8.4+/-2.3)x10^10 Lsun for the detection and L(8-1000um)=(2.9+/-0.9)x10^10 Lsun for the stack. With HST ACS I-band imaging we map the rest-frame UV emission on the same scale as the dust, effectively resolving the 'infrared excess' (IRX=L_FIR/L_UV) in a normal galaxy at z=3. Integrated over the galaxy we measure IRX=0.56+/-0.15, and the galaxy-averaged UV slope is beta=-1.25+/-0.03. This puts the galaxy a factor of ~10 below the IRX-beta relation for local starburst nuclei of Meurer et al. (1999). However, IRX varies by more than a factor of 3 across the galaxy, and we conclude that the complex relative morphology of the dust relative to UV emission is largely responsible for the scatter in the IRX-beta relation at high-z. A naive application of a Meurer-like dust correction based on the UV slope would dramatically over-estimate the total star formation rate, and our results support growing evidence that when integrated over the galaxy, the typical conditions in high-z star-forming galaxies are not analogous to those in the local starburst nuclei used to establish the Meurer relation.

astro-ph.GA↗

arXiv2016

ALMA observations of Lyman-alpha Blob 1: halo sub-structure illuminated from within

We present new Atacama Large Millimeter/Submillimeter Array (ALMA) 850um continuum observations of the original Lyman-alpha Blob (LAB) in the SSA22 field at z=3.1 (SSA22-LAB01). The ALMA map resolves the previously identified submillimeter source into three components with total flux density S_850 = 1.68+/-0.06 mJy, corresponding to a star formation rate of ~150 M_sun/yr. The submillimeter sources are associated with several faint (m~27 mag) rest-frame ultraviolet sources identified in Hubble Space Telescope Imaging Spectrograph (STIS) clear filter imaging (~5850A). One of these companions is spectroscopically confirmed with Keck MOSFIRE to lie within 20 projected kpc and 250 km/s of one of the ALMA components. We postulate that some of these STIS sources represent a population of low-mass star-forming satellites surrounding the central submillimeter sources, potentially contributing to their growth and activity through accretion. Using a high resolution cosmological zoom simulation of a 10^13 M_sun halo at z=3, including stellar, dust and Ly-alpha radiative transfer, we can model the ALMA+STIS observations and demonstrate that Ly-alpha photons escaping from the central submillimeter sources are expected to resonantly scatter in neutral hydrogen, the majority of which is predicted to be associated with halo substructure. We show how this process gives rise to extended Ly-alpha emission with similar surface brightness and morphology to observed giant LABs.

astro-ph.GA↗

arXiv2016

ALMA observations of a z~3.1 Protocluster: Star Formation from Active Galactic Nuclei and Lyman-Alpha Blobs in an Overdense Environment

We exploit ALMA 870um observations to measure the star-formation rates (SFRs) of eight X-ray detected Active Galactic Nuclei (AGNs) in a z~3.1 protocluster, four of which reside in extended Ly-alpha haloes (often termed Ly-alpha blobs: LABs). Three of the AGNs are detected by ALMA and have implied SFRs of ~220-410~M_sun/yr; the non detection of the other five AGNs places SFR upper limits of <210 M_sun/yr. The mean SFR of the protocluster AGNs (~110-210 M_sun/yr) is consistent (within a factor of ~0.7-2.3) with that found for co-eval AGNs in the field, implying that galaxy growth is not significantly accelerated in these systems. However, when also considering ALMA data from the literature, we find evidence for elevated mean SFRs (up-to a factor of ~5.9 over the field) for AGNs at the protocluster core, indicating that galaxy growth is significantly accelerated in the central regions of the protocluster. We also show that all of the four protocluster LABs are associated with an ALMA counterpart within the extent of their Ly-alpha emission. The SFRs of the ALMA sources within the LABs (~150-410 M_sun/yr) are consistent with those expected for co-eval massive star-forming galaxies in the field. Furthermore, the two giant LABs (with physical extents of >100 kpc) do not host more luminous star formation than the smaller LABs, despite being an order of magnitude brighter in Ly-alpha emission. We use these results to discuss star formation as the power source of LABs.

astro-ph.GA↗

arXiv2015

ALMA Deep Field in SSA22: A concentration of dusty starbursts in a z=3.09 protocluster core

We report the results of $1^{\prime}.5 \times3^{\prime}$ mapping at 1.1~mm with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the central region of the $z=3.09$ SSA22 protocluster. By combining our source catalog with archival spectroscopic redshifts, we find that eight submillimeter galaxies (SMGs) with flux densities, $S_{\rm 1.1~mm}=0.7-6.4$~mJy ($L_{\rm IR}\sim10^{12.1}-10^{13.1}L_\odot$) are at $z=3.08-3.10$. Not only are these SMGs members of the protocluster but they in fact reside within the node at the junction of the 50 Mpc-scale filamentary three-dimensional structure traced by Lyman-$α$ emitters (LAEs) in this field. The eight SMGs account for a star formation rate density (SFRD) $\sim$10 $M_\odot$ yr$^{-1}$ Mpc$^{-3}$ in the node, which is two orders of magnitudes higher than the global SFRD at this redshift. We find that four of the eight SMGs host a X-ray luminous active galactic nuclei (AGN). Our results suggest that the vigorous star formation activity and the growth of super massive black holes (SMBHs) occurred simultaneously in the densest regions at $z\sim3$, which may correspond to the most active historical phase of the massive galaxy population found in the core of the clusters in the present universe. Two SMGs are associated with Lyman-$α$ blobs (LABs), implying that the two populations coexist in high density environments for a few cases.

astro-ph.GA↗

arXiv2015

An extremely dense group of massive galaxies at the centre of the protocluster at z = 3.09 in the SSA22 field

We report the discovery of an extremely dense group of massive galaxies at the centre of the protocluster at $z=3.09$ in the SSA22 field from near-infrared spectroscopy conducted with the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) equipped on the Subaru Telecope. The newly discovered group comprises seven galaxies confirmed at $z_{\rm spec}\approx3.09$ within 180 kpc including five massive objects with the stellar masses larger than $10^{10.5}~M_{\odot}$ and is associated with a bright sub-mm source SSA22-AzTEC14. The dynamical mass of the group estimated from the line-of-sight velocity dispersion of the members is $M_{\rm dyn}\sim1.6\pm0.3\times10^{13}~M_{\odot}$. Such a dense group is expected to be very rare at high redshift as we found only a few comparable systems in large-volume cosmological simulations. Such rare groups in the simulations are hosted in collapsed halos with $M_{\rm vir}=10^{13.4}-10^{14.0}~M_{\odot}$ and evolve into the brightest cluster galaxies (BCGs) of the most massive clusters at present. The observed AzTEC14 group at $z=3.09$ is therefore very likely to be a proto-BCG in the multiple merger phase. The observed total stellar mass of the group is $5.8^{+5.1}_{-2.0}\times10^{11}~M_{\odot}$. It suggests that over half the stellar mass of its descendant had been formed by $z=3$. Moreover, we identified over two members for each of the four Ly$α$ blobs (LABs) using our new spectroscopic data. This verifies our previous argument that many of the LABs in the SSA22 protocluster associated with multiple developed stellar components.

astro-ph.GA↗

arXiv2015

Photospheric Flow Field Related to the Evolution of the Sun's Polar Magnetic Patches Observed by Hinode SOT

We investigated the role of photospheric plasma motions in the formation and evolution of polar magnetic patches using time-sequence observations with high spatial resolution. The observations were obtained with the spectropolarimeter on board the Hinode satellite. From the statistical analysis using 75 magnetic patches, we found that they are surrounded by strong converging, supergranulation associated flows during their apparent life time and that the converging flow around the patch boundary is better observed in the Doppler velocity profile in the deeper photosphere. Based on our analysis we suggest that the like-polarity magnetic fragments in the polar region are advected and clustered by photospheric converging flows thereby resulting in the formation of polar magnetic patches. Our observations show that, in addition to direct cancellation magnetic patches decay by fragmentation followed by unipolar disappearance or unipolar disappearance without fragmentation. It is possible that the magnetic patches of existing polarity fragment or diffuse away into smaller elements and eventually cancel out with opposite polarity fragments that reach the polar region around solar cycle maximum. This could be one of the possible mechanisms by which the existing polarity decay during the reversal of the polar magnetic field.

astro-ph.SR↗

arXiv2014

Ly-alpha polarimeter design for CLASP rocket experiment

A sounding-rocket program called the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is proposed to be launched in the summer of 2014. CLASP will observe the solar chromosphere in Ly-alpha (121.567 nm), aiming to detect the linear polarization signal produced by scattering processes and the Hanle effect for the first time. The polarimeter of CLASP consists of a rotating half-waveplate, a beam splitter, and a polarization analyzer. Magnesium Fluoride (MgF2) is used for these optical components, because MgF2 exhibits birefringent property and high transparency at ultraviolet wavelength.

astro-ph.IM↗

arXiv2014

AzTEC/ASTE 1.1 mm survey of SSA22: Counterpart identification and photometric redshift survey of submillimeter galaxies

We present the results from a 1.1 mm imaging survey of the SSA22 field, known for having an overdensity of z=3.1 Lyman-alpha emitting galaxies (LAEs), taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE). We imaged a 950 arcmin$^2$ field down to a 1 sigma sensitivity of 0.7-1.3 mJy/beam to find 125 submillimeter galaxies (SMGs) with a signal to noise ratio >= 3.5. Counterpart identification using radio and near/mid-infrared data was performed and one or more counterpart candidates were found for 59 SMGs. Photometric redshifts based on optical to near-infrared images were evaluated for 45 SMGs of these SMGs with Spitzer/IRAC data, and the median value is found to be z=2.4. By combining these estimation with estimates from the literature we determined that 10 SMGs might lie within the large-scale structure at z=3.1. The two-point angular cross-correlation function between LAEs and SMGs indicates that the positions of the SMGs are correlated with the z=3.1 protocluster. These results suggest that the SMGs were formed and evolved selectively in the high dense environment of the high redshift universe. This picture is consistent with the predictions of the standard model of hierarchical structure formation.

astro-ph.CO↗

arXiv2013

All-optical sensing of a single-molecule electron spin

We demonstrate an all-optical method for magnetic sensing of individual molecules in ambient conditions at room temperature. Our approach is based on shallow nitrogen-vacancy (NV) centers near the surface of a diamond crystal, which we use to detect single paramagnetic molecules covalently attached to the diamond surface. The manipulation and readout of the NV centers is all-optical and provides a sensitive probe of the magnetic field fluctuations stemming from the dynamics of the electronic spins of the attached molecules. As a specific example, we demonstrate detection of a single paramagnetic molecule containing a gadolinium (Gd$^{3+}$) ion. We confirm single-molecule resolution using optical fluorescence and atomic force microscopy to co-localize one NV center and one Gd$^{3+}$-containing molecule. Possible applications include nanoscale and in vivo magnetic spectroscopy and imaging of individual molecules.

cond-mat.mes-hall↗

arXiv2013

The Association of Polar Faculae with Polar Magnetic Patches Examined with Hinode Observations

The magnetic properties of the Sun's polar faculae are investigated with spectropolarimetric observations of the north polar region obtained by the Hinode satellite in 2007 September. Polar faculae are embedded in nearly all magnetic patches with fluxes greater than $10^{18}$ Mx, while magnetic patches without polar faculae dominate in the flux range below $10^{18}$ Mx. The faculae are considerably smaller than their parent patches, and single magnetic patches contain single or multiple faculae. The faculae in general have higher intrinsic magnetic field strengths than the surrounding regions within their parent patches. Less than 20% of the total magnetic flux contributed by the large (${\ge}10^{18}$ Mx) concentrations, which are known to be modulated by the solar cycle, is accounted for by the associated polar faculae.

astro-ph.SR↗

arXiv2013

Nanometer scale quantum thermometry in a living cell

Sensitive probing of temperature variations on nanometer scales represents an outstanding challenge in many areas of modern science and technology. In particular, a thermometer capable of sub-degree temperature resolution as well as integration within a living system could provide a powerful new tool for many areas of biological research, including temperature-induced control of gene expression and cell-selective treatment of disease. Here, we demonstrate a new approach to nanoscale thermometry that utilizes coherent manipulation of the electronic spin associated with nitrogen-vacancy (NV) color centers in diamond. We show the ability to detect temperature variations down to 1.8 mK (sensitivity of 9 mK/sqrt(Hz)) in an ultra-pure bulk diamond sample. Using NV centers in diamond nanocrystals (nanodiamonds), we directly measure the local thermal environment at length scales down to 200 nm. Finally, by introducing both nanodiamonds and gold nanoparticles into a single human embryonic fibroblast, we demonstrate temperature-gradient control and mapping at the sub-cellular level, enabling unique potential applications in life sciences.

quant-ph↗

arXiv2011

Temporal Relation between Disappearance of Penumbral Fine-Scale Structure and Evershed Flow

We investigate the temporal relation between the Evershed flow, dot-like bright features (penumbral grain), the complex magnetic field structure, and dark lanes (dark core) along bright filaments in a sunspot penumbra. We use a time series of high spatial resolution photospheric intensity, vector magnetic field maps, and Doppler velocity maps obtained with the Solar Optical Telescope aboard the \textit{Hinode} spacecraft. We conclude that the appearance and disappearance of the Evershed flow and penumbra grains occur at nearly the same time and are associated with changes of the inclination angle of the magnetic field from vertical to more horizontal. This supports the idea that Evershed flow is a result of thermal convection in the inclined field lines. The dark core of the bright penumbral filament also appears coincidental with the Evershed flow. However, the dark-cored bright filament survives at least for 10-20 minutes after the disappearance of the Evershed flow. The heat input into the bright filament continues after the end of heat transfer by the Evershed flow. This suggests that local heating along the bright filament is important to maintain the brightness of the bright filament in addition to the heat transfer by the Evershed flow.

astro-ph.SR↗