arXiv subjects

Yun-Hsin Huang

Publications and source records attributed to Yun-Hsin Huang.

15 recordsLinked to original sources

arXiv2024

MOSA: Music Motion with Semantic Annotation Dataset for Cross-Modal Music Processing

In cross-modal music processing, translation between visual, auditory, and semantic content opens up new possibilities as well as challenges. The construction of such a transformative scheme depends upon a benchmark corpus with a comprehensive data infrastructure. In particular, the assembly of a large-scale cross-modal dataset presents major challenges. In this paper, we present the MOSA (Music mOtion with Semantic Annotation) dataset, which contains high quality 3-D motion capture data, aligned audio recordings, and note-by-note semantic annotations of pitch, beat, phrase, dynamic, articulation, and harmony for 742 professional music performances by 23 professional musicians, comprising more than 30 hours and 570 K notes of data. To our knowledge, this is the largest cross-modal music dataset with note-level annotations to date. To demonstrate the usage of the MOSA dataset, we present several innovative cross-modal music information retrieval (MIR) and musical content generation tasks, including the detection of beats, downbeats, phrase, and expressive contents from audio, video and motion data, and the generation of musicians' body motion from given music audio. The dataset and codes are available alongside this publication (https://github.com/yufenhuang/MOSA-Music-mOtion-and-Semantic-Annotation-dataset).

cs.SD↗

arXiv2021

Spectroscopic Confirmation of two Extremely Massive Protoclusters BOSS1244 and BOSS1542 at $z=2.24$

We present spectroscopic confirmation of two new massive galaxy protoclusters at $z=2.24\pm0.02$, BOSS1244 and BOSS1542, traced by groups of Coherently Strong Ly$α$ Absorption (CoSLA) systems imprinted in the absorption spectra of a number of quasars from the SDSS III and identified as overdensities of narrowband-selected H$α$ emitters (HAEs). Using MMT/MMIRS and LBT/LUCI near-infrared (NIR) spectroscopy, we confirm 46 and 36 HAEs in the BOSS1244 and BOSS1542 fields, respectively. BOSS1244 displays a South-West (SW) component at $z=2.230\pm0.002$ and another North-East (NE) component at $z=2.246\pm0.001$ with the line-of-sight velocity dispersions of $405\pm202$ km s$^{-1}$ and $377\pm99$ km s$^{-1}$, respectively. Interestingly, we find that the SW region of BOSS1244 contains two substructures in redshift space, likely merging to form a larger system. In contrast, BOSS1542 exhibits an extended filamentary structure with a low velocity dispersion of $247\pm32$ km s$^{-1}$ at $z=2.241\pm0.001$, providing a direct confirmation of a large-scale cosmic web in the early Universe. The galaxy overdensities $δ_{\rm g}$ on the scale of 15 cMpc are $22.9\pm4.9$, $10.9\pm2.5$, and $20.5\pm3.9$ for the BOSS1244 SW, BOSS1244 NE, and BOSS1542 filament, respectively. They are the most overdense galaxy protoclusters ($δ_{\rm g}>20$) discovered to date at $z>2$. These systems are expected to become virialized at $z\sim0$ with a total mass of $M_{\rm SW}=(1.59\pm0.20)\times10^{15}$ $M_{\odot}$, $M_{\rm NE} =(0.83\pm0.11)\times10^{15}$ $M_{\odot}$ and $M_{\rm filament}=(1.42\pm0.18)\times10^{15}$ $M_{\odot}$, respectively. Together with BOSS1441 described in Cai et al. (2017a), these extremely massive overdensities at $z=2-3$ exhibit different morphologies, indicating that they are in different assembly stages in the formation of early galaxy clusters.

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arXiv2021

A Complete Census of Circumgalactic MgII at Redshift z<~ 0.5

We present a survey of MgII absorbing gas in the vicinity of 380 random galaxies, using 156 background quasi-stellar objects(QSOs) as absorption-line probes. The sample comprises 211 isolated (73 quiescent and 138 star-forming galaxies) and 43 non-isolated galaxies with sensitive constraints for both MgII absorption and Ha emission. The projected distances span a range from d=9 to 497 kpc, redshifts of the galaxies range from z=0.10 to 0.48, and rest-frame absolute B-band magnitudes range from $M_{\rm B}=-16.7$ to $-22.8$. Our analysis shows that the rest-frame equivalent width of MgII, $W_r$(2796), depends on halo radius($R_h$), $B$-band luminosity($L_{\rm B}$) and stellar mass ($M_{\rm star}$) of the host galaxies, and declines steeply with increasing $d$ for isolated, star-forming galaxies. $W_r$(2796) exhibits no clear trend for either isolated, quiescent galaxies or non-isolated galaxies. The covering fraction of MgII absorbing gas $\langle κ\rangle$ is high with $\langle κ\rangle\gtrsim 60$% at $<40$ kpc for isolated galaxies and declines rapidly to $\langle κ\rangle\approx 0$ at $d\gtrsim100$ kpc. Within the gaseous radius, $\langle κ\rangle$ depends sensitively on both $M_{\rm star}$ and the specific star formation rate inferred from Ha. Different from massive quiescent halos, the observed velocity dispersion of MgII gas around star-forming galaxies is consistent with expectations from virial motion, which constrains individual clump mass to $m_{\rm cl} \gtrsim 10^5 \,\rm M_\odot$ and cool gas accretion rate of $\sim 0.7-2 \,M_\odot\,\rm yr^{-1}$. We find no strong azimuthal dependence of MgII absorption for either star-forming or quiescent galaxies. Our results highlight the need of a homogeneous, absorption-blind sample for establishing a holistic description of chemically-enriched gas in the circumgalactic space.

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arXiv2020

A Closer Look at Two of the Most Luminous Quasars in the Universe

Ultra-luminous quasars ($M_{1450} \leq -29$) provide us with a rare view into the nature of the most massive and most rapidly accreting supermassive black holes (SMBHs). Following the discovery of two of these extreme sources, J0341${+}$1720 ($M_{1450}=-29.56$, $z=3.71$) and J2125${-}$1719 ($M_{1450}=-29.39$, $z=3.90$), in the Extremely Luminous Quasar Survey (ELQS) and its extension to the Pan-STARRS\,1 footprint (PS-ELQS), we herein present an analysis of their rest-frame UV to optical spectroscopy. Both quasars harbor very massive SMBHs with $M_{\rm{BH}}=6.73_{-0.83}^{+0.75}\times10^{9}\,M_{\odot}$ and $M_{\rm{BH}}=5.45_{-0.55}^{+0.60}\times10^{9}\,M_{\odot}$, respectively, showing evidence of accretion above the Eddington limit ($L_{\rm{bol}}/L_{\rm{Edd}}=2.74_{-0.27}^{+0.39}$ and $L_{\rm{bol}}/L_{\rm{Edd}}=3.01_{-0.30}^{+0.34}$). NOEMA 3 millimeter observations of J0341${+}$1720 reveal a highly star-forming ($\rm{SFR}\approx1500\,M_{\odot}\,\rm{yr}^{-1}$), ultra-luminous infrared galaxy ($L_{\rm{TIR}}\approx1.0\times10^{13}\,L_{\odot}$) host, which, based on an estimate of its dynamical mass, is only ${\sim}30$ times more massive than the SMBH it harbors at its center. As examples of luminous super-Eddington accretion, these two quasars provide support for theories, which explain the existence of billion solar mass SMBHs ${\sim}700$ million years after the Big Bang by moderate super-Eddington growth from standard SMBH seeds.

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arXiv2019

Quasars Have Fewer Close Companions than Normal Galaxies

We investigate the distribution of companion galaxies around quasars using {\em Hubble Space Telescope} ({\em HST}) Advanced Camera for Surveys Wide Field Camera (ACS/WFC) archival images. Our master sample contains 532 quasars which have been observed by {\em HST} ACS/WFC, spanning a wide range of luminosity $(-31 90\%)$ even for the faintest companions of interest. The number of physical companions is estimated by subtracting a background density from the number density of projected companions. We divide all the companions into three groups (faint, intermediate and bright) according to their fluxes. A control sample of galaxies is constructed to have similar redshift distribution and stellar mass range as the quasar sample using the data from {\em HST} deep fields. We find that quasars and control sample galaxies have similar numbers of faint and bright companions, while quasars show a $3.7σ$ deficit of intermediate companions compared to galaxies. The numbers of companions in all three groups do not show strong evolution with redshift, and the number of intermediate companions around quasars decreases with quasar luminosity. Assuming that merger-triggered quasars have entered the final coalescence stage during which individual companions are no longer detectable at large separations, our result is consistent with a picture in which a significant fraction of quasars is triggered by mergers.

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arXiv2019

The Extremely Luminous Quasar Survey in the Pan-STARRS 1 Footprint (PS-ELQS)

We present the results of the Extremely Luminous Quasar Survey in the $3π$ survey of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS; PS1). This effort applies the successful quasar selection strategy of the Extremely Luminous Survey in the Sloan Digital Sky Survey footprint ($\sim12,000\,\rm{deg}^2$) to a much larger area ($\sim\rm{21486}\,\rm{deg}^2$). This spectroscopic survey targets the most luminous quasars ($M_{1450}\le-26.5$; $m_{i}\le18.5$) at intermediate redshifts ($z\ge2.8$). Candidates are selected based on a near-infrared JKW2 color cut using WISE AllWISE and 2MASS photometry to mainly reject stellar contaminants. Photometric redshifts ($z_{\rm{reg}}$) and star-quasar classifications for each candidate are calculated from near-infrared and optical photometry using the supervised machine learning technique random forests. We select 806 quasar candidates at $z_{\rm{reg}}\ge2.8$ from a parent sample of 74318 sources. After exclusion of known sources and rejection of candidates with unreliable photometry, we have taken optical identification spectra for 290 of our 334 good PS-ELQS candidates. We report the discovery of 190 new $z\ge2.8$ quasars and an additional 28 quasars at lower redshifts. A total of 44 good PS-ELQS candidates remain unobserved. Including all known quasars at $z\ge2.8$, our quasar selection method has a selection efficiency of at least $77\%$. At lower declinations $-30\le\rm{Decl.}\le0$ we approximately triple the known population of extremely luminous quasars. We provide the PS-ELQS quasar catalog with a total of 592 luminous quasars ($m_{i}\le18.5$, $z\ge2.8$). This unique sample will not only be able to provide constraints on the volume density and quasar clustering of extremely luminous quasars, but also offers valuable targets for studies of the intergalactic medium.

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arXiv2019

Characterizing Circumgalactic Gas around Massive Ellipticals at z~0.4 - II. Physical Properties and Elemental Abundances

We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d<160 kpc of luminous red galaxies (LRGs). The sample comprises 16 intermediate-redshift (z=0.21-0.55) LRGs of stellar mass M_star>1e11 M_sun. Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full HI Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually-matched components, we show that cool gas (T~1e4 K) density and metallicity can vary by more than a factor of ten in in an LRG halo. Specifically, metal-poor absorbing components with <1/10 solar metallicity are seen in 50% of the LRG halos, while gas with solar and super-solar metallicity is also common. These results indicate a complex multiphase structure and poor chemical mixing in these quiescent halos. We calculate the total surface mass density of cool gas, Σ_cool, by applying the estimated ionization fraction corrections to the observed HI column densities. The radial profile of Σ_cool is best-described by a projected Einasto profile of slope α=1 and scale radius r_s=48 kpc. We find that typical LRGs at z~0.4 contain cool gas mass of M_cool= (1-2) x1e10 M_sun at d<160 kpc (or as much as 4x1e10 M_sun at d<500 kpc), comparable to the cool CGM mass of star-forming galaxies. Furthermore, we show that high-ionization OVI and low-ionization absorption species exhibit distinct velocity profiles, highlighting their different physical origins. We discuss the implications of our findings for the origin and fate of cool gas in LRG halos.

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arXiv2018

The Extremely Luminous Quasar Survey in the Sloan Digital Sky Survey footprint. III. The South Galactic Cap Sample and the Quasar Luminosity Function at Cosmic Noon

We have designed the Extremely Luminous Quasar Survey (ELQS) to provide a highly complete census of unobscured UV-bright quasars during the cosmic noon, $z=2.8-5.0$. Here we report the discovery of 70 new quasars in the ELQS South Galactic Cap (ELQS-S) quasar sample, doubling the number of known extremely luminous quasars in $4,237.3\,\rm{deg}^2$ of the SDSS footprint. These observations conclude the ELQS and we present the properties of the full ELQS quasar catalog, containing 407 quasars over $11,838.5\,\rm{deg}^2$. Our novel ELQS quasar selection strategy resulted in unprecedented completeness at the bright end and allowed us to discover 109 new quasars in total. This marks an increase of $\sim36\%$ (109/298) to the known population at these redshifts and magnitudes, while we further are able to retain a selection efficiency of $\sim80\%$. On the basis of 166 quasars from the full ELQS quasar catalog, who adhere to the uniform criteria of the 2MASS point source catalog, we measure the bright-end quasar luminosity function (QLF) and extend it one magnitude brighter than previous studies. Assuming a single power law with exponential density evolution for the functional form of the QLF, we retrieve the best fit parameters from a maximum likelihood analysis. We find a steep bright-end slope of $β\approx-4.1$ and we can constrain the bright-end slope to $β\leq-3.4$ with $99\%$ confidence. The density is well modeled by the exponential redshift evolution, resulting in a moderate decrease with redshift ($γ\approx-0.4$).

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arXiv2018

The Discovery of A Luminous Broad Absorption Line Quasar at A Redshift of 7.02

Despite extensive efforts, only two quasars have been found at $z>7$ to date due to a combination of low spatial density and high contamination from more ubiquitous Galactic cool dwarfs in quasar selection. This limits our current knowledge of the super-massive black hole (SMBH) growth mechanism and reionization history. In this letter, we report the discovery of a luminous quasar at $z=7.021$, DELS J003836.10$-$152723.6 (hereafter J0038$-$1527), selected using photometric data from DESI Legacy imaging Survey (DELS), Pan-STARRS1 (PS1) imaging Survey, as well as Wide-field Infrared Survey Explore ($WISE$) mid-infrared all-sky survey. With an absolute magnitude of $M_{1450}$=$-$27.1 and bolometric luminosity of $L_{\rm Bol}$=5.6$\times$10$^{13}$ $L_\odot$, J0038$-$1527 is the most luminous quasar known at $z>7$. Deep optical to near infrared spectroscopic observations suggest that J0038-1527 hosts a 1.3 billion solar mass BH accreting at the Eddington limit, with an Eddington ratio of 1.25$\pm$0.19. The CIV broad emission line of J0038$-$1527 is blue-shifted by more than 3000 km s$^{-1}$ to the systemic redshift. More detailed investigations of the high quality spectra reveal three extremely high velocity CIV broad absorption lines (BALs) with velocity from 0.08 to 0.14 times the speed of light and total balnicity index of more than 5000 km s$^{-1}$, suggesting the presence of relativistic outflows. J0038$-$1527 is the first quasar found at the epoch of reionization (EoR) with such strong outflows and provides a unique laboratory to investigate AGN feedback on the formation and growth of the most massive galaxies in the early universe.

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arXiv2018

Exploring Reionization-Era Quasars III: Discovery of 16 Quasars at $6.4\lesssim z \lesssim 6.9$ with DESI Legacy Imaging Surveys and UKIRT Hemisphere Survey and Quasar Luminosity Function at $z\sim6.7$

This is the third paper in a series aims at finding reionzation-era quasars with the combination of DESI Legacy imaging Surveys (DELS) and near-infrared imaging surveys, such as the UKIRT Hemisphere Survey (UHS), as well as the Wide-field Infrared Survey Explore ($WISE$) mid-infrared survey. In this paper, we describe the updated quasar candidate selection procedure, report the discovery of 16 quasars at $6.4\lesssim z \lesssim6.9$ from area of $\sim$13,020 deg$^2$, and present the quasar luminosity function (QLF) at $z\sim6.7$. The measured QLF follows $Φ(L_{1450})\propto L_{1450}^{-2.35}$ in the magnitude range $27.6<M_{1450}<-25.5$. We determine the quasar comoving spatial density at $\langle z \rangle$=6.7 and $M_{1450}<-26.0$ to be $\rm 0.39\pm0.11 Gpc^{-3}$ and find that the exponential density evolution parameter to be $k=-0.78\pm0.18$ from $z\sim6$ to $z\sim6.7$, corresponding to a rapid decline by a factor of $\sim 6$ per unit redshift towards earlier epoch, a rate significantly faster than that at $z\sim 3- 5$. The cosmic time between $z\sim6$ and $z\sim6.7$ is only 121 Myrs. The quasar density declined by a factor of more than three within such short time requires that SMBHs must grow rapidly or they are less radiatively efficient at higher redshifts. We measured quasar comoving emissivity at $z\sim6.7$ which indicate that high redshift quasars are highly unlikely to make a significant contribution to hydrogen reionization. The broad absorption line (BAL) quasar fraction at $z\gtrsim6.5$ is measured to be $\gtrsim$22%. In addition, we also report the discovery of additional five quasars at $z\sim6$ in the appendix.

astro-ph.GA↗

arXiv2018

The Extremely Luminous Quasar Survey (ELQS) in the Sloan Digital Sky Survey footprint. II. The North Galactic Cap Sample

We present the North Galactic Cap sample of the Extremely Luminous Quasar Survey (ELQS-N), which targets quasars with $M_{1450}<-27$ at $2.8 \leq z < 5$ in an area of $\sim7600\,\rm{deg}^2$ of the Sloan Digital Sky Survey (SDSS) footprint with $90\text{\textdegree}<\rm{RA}<270\text{\textdegree}$. Based on a near-infrared/infrared \textit{JKW2} color cut, the ELQS selection efficiently uses random forest methods to classify quasars and to estimate photometric redshifts; this scheme overcomes some of the difficulties of pure optical quasar selection at $z\approx3$. As a result, we retain a completeness of $>70\%$ over $z\sim3.0-5.0$ at $m_{i}\lesssim17.5$, limited toward fainter magnitudes by the depth of the Two Micron All Sky Survey (2MASS). The presented quasar catalog consists of a total of 270 objects, of which 39 are newly identified in this work with spectroscopy obtained at the Vatican Advanced Technology Telescope and the MMT $6.5\,\rm{m}$ telescope. In addition to the high completeness, which allowed us to discover new quasars in the already well-surveyed SDSS North Galactic Cap, the efficiency of our selection is relatively high at $\sim79\%$. Using 120 objects of this quasar sample we are able to extend the previously measured optical quasar luminosity function (QLF) by one magnitude toward the bright end at $2.8 \leq z \leq 4.5$. A first analysis of the QLF suggests a relatively steep bright-end slope of $β\approx-4$ for this sample. This result contrasts with previous results in the same redshift range, which find a much flatter slope around $β\sim-2.5$, but agrees with recent measurements of the bright-end slope at lower and higher redshifts. Our results constrain the bright-end slope at $z=2.8-4.5$ to $β<-2.94$ with a 99\% confidence.

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arXiv2018

Characterizing Circumgalactic Gas around Massive Ellipticals at z ~ 0.4 I. Initial Results

We present a new Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) absorption-line survey to study halo gas around 16 luminous red galaxies (LRGs) at z=0.21-0.55. The LRGs are selected uniformly with stellar mass Mstar>1e11 Msun and no prior knowledge of the presence/absence of any absorption features. Based on observations of the full Lyman series, we obtain accurate measurements of neutral hydrogen column density N(HI) and find that high-N(HI) gas is common in these massive quiescent halos with a median of = 16.6 at projected distances d<~160 kpc. We measure a mean covering fraction of optically-thick gas with log N(HI)>~17.2 of LLS=0.44^{+0.12}_{-0.11} at d<~160 kpc and LLS=0.71^{+0.11}_{-0.20} at d<~100 kpc. The line-of-sight velocity separations between the HI absorbing gas and LRGs are characterized by a mean and dispersion of =29 km/s and σ_v_{gas-gal}=171 km/s. Combining COS FUV and ground-based echelle spectra provides an expanded spectral coverage for multiple ionic transitions, from low-ionization MgII and SiII, to intermediate ionization SiIII and CIII, and to high-ionization OVI absorption lines. We find that intermediate ions probed by CIII and SiIII are the most prominent UV metal lines in LRG halos with a mean covering fraction of _{0.1}=0.75^{+0.08}_{-0.13} for W(977)>=0.1 Ang at d<160 kpc, comparable to what is seen for CIII in L* and sub-L* star-forming and red galaxies but exceeding MgII or OVI in quiescent halos. The COS-LRG survey shows that massive quiescent halos contain widespread chemically-enriched cool gas and that little distinction between LRG and star-forming halos is found in their HI and CIII content.

astro-ph.GA↗

arXiv2016

On Detecting Halo Assembly Bias with Galaxy Populations

The fact that the clustering of dark matter halos depends not only on their mass, but also the formation epoch, is a prominent, albeit subtle, feature of the cold dark matter structure formation theory, and is known as assembly bias. At low mass scales ($\sim 10^{12}\,h^{-1}M_\odot$), early-forming halos are predicted to be more strongly clustered than the late-forming ones. In this study we aim to robustly detect the signature of assembly bias observationally, making use of formation time indicators of central galaxies in low mass halos as a proxy for the halo formation history. Weak gravitational lensing is employed to ensure our early- and late-forming halo samples have similar masses, and are free of contamination of satellites from more massive halos. For the two formation time indicators used (resolved star formation history and current specific star formation rate), we do not find convincing evidence of assembly bias. For a pair of early- and late-forming galaxy samples with mean mass $M_{200c} \approx 9\times10^{11}\,h^{-1}M_\odot$, the relative bias is $1.00\pm 0.12$. We attribute the lack of detection to the possibilities that either the current measurements of these indicators are too noisy, or they do not correlate well with the halo formation history. Alternative proxies for the halo formation history that should perform better are suggested for future studies.

astro-ph.GA↗

arXiv2015

Characterizing the Chemically-Enriched Circumgalactic Medium of ~38000 Luminous Red Galaxies in SDSS DR12

We report a definitive detection of chemically-enriched cool gas around massive, quiescent galaxies at z~0.4-0.7. The result is based on a survey of 37621 luminous red galaxy (LRG)-QSO pairs in SDSS DR12 with projected distance d<500 kpc. The LRGs are characterized by a predominantly old (age>~1Gyr) stellar population with 13% displaying [OII] emission features and LINER-like spectra. Both passive and [OII]-emitting LRGs share the same stellar mass distribution with a mean of ~11.4 and a dispersion of 0.2 dex. Both LRG populations exhibit associated strong MgII absorbers out to d<500 kpc. The mean gas covering fraction at d<~120 kpc is _MgII > 15% and declines quickly to _MgII ~ 5% at d<~500 kpc. No clear dependence on stellar mass is detected for the observed MgII absorption properties. The observed velocity dispersion of MgII absorbing gas relative to either passive or [OII]-emitting LRGs is merely 60% of what is expected from virial motion in these massive halos. While no apparent azimuthal dependence is seen for _MgII around passive LRGs at all radii, a modest enhancement in _MgII is detected along the major axis of [OII]-emitting LRGs at d<50 kpc. The suppressed velocity dispersion of MgII absorbing gas around both passive and [OII]-emitting LRGs, together with an elevated _MgII along the major axis of [OII]-emitting LRGs at d<50 kpc, provides important insights into the origin of the observed chemically-enriched cool gas in LRG halos. We consider different scenarios and conclude that the observed MgII absorbers around LRGs are best-explained by a combination of cool clouds formed in thermally unstable LRG halos and satellite accretion through filaments.

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arXiv2013

Probing the Earliest Stage of Protostellar Evolution -- Barnard 1-bN and Barnard 1-bS

Two submm/mm sources in the Barnard 1b (B1-b) core, B1-bN and B1-bS, have been observed with the Submillimeter Array (SMA) and the Submillimeter Telescope (SMT). The 1.1 mm continuum map obtained with the SMA reveals that the two sources contain spatially compact components, suggesting that they harbor protostars. The N2D+ and N2H+ J=3-2 maps were obtained by combining the SMA and SMT data. The N2D+ map clearly shows two peaks at the continuum positions. The N2H+ map also peaks at the continuum positions, but is more dominated by the spatially extended component. The N2D+/N2H+ ratio was estimated to be ~ 0.2 at the positions of both B1-bN and B1-bS. The derived N2D+/N2H+ ratio is comparable to those of the prestellar cores in the late evolutionary stage and the class 0 protostars in the early evolutionary stage. Although B1-bN is bright in N2H+ and N2D+, this source was barely seen in H13CO+. This implies that the depletion of carbon-bearing molecules is significant in B1-bN. The chemical property suggests that B1-bN is in the earlier evolutionary stage as compared to B1-bS with the H13CO+ counterpart. The N2H+ and N2D+ lines show that the radial velocities of the two sources are different by ~ 0.9 km s-1. However, the velocity pattern along the line through B1-bN and B1-bS suggests that these two sources were not formed out of a single rotating cloud. It is likely that the B1-b core consists of two velocity components, each of which harbors a very young source.

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