arXiv subjects

Zheng Cai

Publications and source records attributed to Zheng Cai.

At least 199 records · Page 11Linked to original sources

arXiv2017

Glyph-aware Embedding of Chinese Characters

Given the advantage and recent success of English character-level and subword-unit models in several NLP tasks, we consider the equivalent modeling problem for Chinese. Chinese script is logographic and many Chinese logograms are composed of common substructures that provide semantic, phonetic and syntactic hints. In this work, we propose to explicitly incorporate the visual appearance of a character's glyph in its representation, resulting in a novel glyph-aware embedding of Chinese characters. Being inspired by the success of convolutional neural networks in computer vision, we use them to incorporate the spatio-structural patterns of Chinese glyphs as rendered in raw pixels. In the context of two basic Chinese NLP tasks of language modeling and word segmentation, the model learns to represent each character's task-relevant semantic and syntactic information in the character-level embedding.

cs.CL↗

arXiv2017

Scientific performance analysis of the SYZ telescope design vs. the RC telescope design

Recently, Su et al. (2016) propose a telescope design, referred as the "SYZ" design, for Chinese new project of a 12m optical-infrared telescope. The SYZ telescope design consists of three aspheric mirrors with non-zero power, including a relay mirror below the primary mirror. SYZ design yields a good imaging quality and has a relatively flat field curvature at Nasmyth focus. To evaluate the science-compatibility of this three-mirror telescope, in this paper, we thoroughly compare the performance of SYZ design with that of Ritchey-Chrétien (RC) design, a conventional two-mirror telescope design. Further, we propose the Observing Information Throughput ($OIT$) as a metric for quantitatively evaluating the telescopes' science performance. We find that although a SYZ telescope yields a superb imaging quality over a large field of view, a two-mirror (RC) telescope design holds a higher overall throughput, a better diffraction-limited imaging quality in the central field of view (FOV$<5'$) which is better for the performance of extreme Adaptive Optics (AO), and a generally better scientific performance with a higher $OIT$ value.

astro-ph.IM↗

arXiv2017

Constraining C iii] Emission in a Sample of Five Luminous z = 5.7 Galaxies

Recent observations have suggested that the CIII]$\lambda1907/1909$ emission lines could be alternative diagnostic lines for galaxies in the reionization epoch. We use the F128N narrowband filter on the Hubble Space Telescope's ($\it{HST}$) Wide Field Camera 3 (WFC3) to search for CIII] emission in a sample of five galaxies at z = 5.7 in the Subaru Deep Field and the Subaru/XMM-Newton Deep Field. Using the F128N narrowband imaging, together with the broadband imaging, we do not detect CIII] emission for the five galaxies with $J_{\rm{AB}}$ ranging from 24.10 -- 27.00 in our sample. For the brightest galaxy J132416.13+274411.6 in our sample (z = 5.70, $J_{\rm{AB}} = 24.10$), which has a significantly higher signal to noise, we report a CIII] flux of $3.34\pm1.81 \times 10^{-18}$ $\mathrm{erg\ s^{-1}\ cm^{-2}}$, which places a stringent 3-$\rmσ$ upper limit of $5.43\times 10^{-18}$ $\mathrm{erg\ s^{-1}\ cm^{-2}}$ on CIII] flux and 6.57 Å on the CIII] equivalent width. Using the stacked image, we put a 3-$\rmσ$ upper limit on the mean CIII] flux of $\mathrm{2.55\times10^{-18}\ erg\ s^{-1}\ cm^{-2}}$, and a 3-$\rmσ$ upper limit on the mean CIII] equivalent width of 4.20 Å for this sample of galaxies at z = 5.70. Combined with strong CIII] detection reported among high-z galaxies in the literature, our observations suggest that the equivalent widths of CIII] from galaxies at z $>$ 5.70 exhibit a wide range of distribution. Our strong limits on CIII] emission could be used as a guide for future observations in the reionization epoch.

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arXiv2017

High Lyman Continuum Escape Fraction in a Lensed Young Compact Dwarf Galaxy at $z=2.5$

We present the HST WFC3/F275W UV imaging observations of A2218-Flanking, a lensed compact dwarf galaxy at redshift $z\approx2.5$. The stellar mass of A2218-Flanking is $\log(M/M_{\odot}=9.14$ and SFR is 12.5$M_\odot$yr$^{-1}$ after correcting the magnification. This galaxy has a young galaxy age of 127 Myr and a compact galaxy size of $r_{1/2}=2.4$kpc. The HST UV imaging observations cover the rest-frame Lyman continuum (LyC) emission ($\sim800$Å) from A2218-Flanking. We firmly detect ($14σ$) the LyC emission in A2218-Flanking in the F275W image. Together with the HST F606W images, we find that the absolute escape fraction of LyC is $f_{\rm abs,esc}>28-57\%$ based on the flux density ratio between 1700Å and 800Å ($f_{1700}/f_{800}$). The morphology of the LyC emission in the F275W images is extended and well follows the morphology of the UV continuum morphology in the F606W images, suggesting that the $f_{800}$ is not from foreground contaminants. We find that the region with a high star formation rate surface density has a lower $f_{1700}/f_{800}$ (higher $f_{800}/f_{1700}$) ratio than the diffused regions, suggesting that LyC photons are more likely to escape from the region with the intensive star-forming process. We compare the properties of galaxies with and without LyC detections and find that LyC photons are easier to escape in low mass galaxies.

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arXiv2017

A Ringed Dwarf LINER 1 Galaxy Hosting an Intermediate-mass Black Hole with Large-scale Rotation-like Hα Emission

We report the discovery of a 20-kpc-sized Hα emission in SDSS J083803.68+540642.0, a ringed dwarf galaxy (M$_V$ = -17.89 mag) hosting an accreting intermediate-mass black hole at z=0.02957. Analysis of the HST images indicates that it is an early-type galaxy with a featureless low-surface brightness disk (μ0 = 20.39 mag arcsec$^{-2}$ in the V band) and a prominent, relatively red bulge (V - I = 2.03, Re = 0.28 kpc or 0."48) that accounts for ~81% of the total light in the I band. A circumgalactic ring of a diameter 16 kpc is also detected, with a disperse shape on its south side. The optical emission lines reveal the nucleus to be a broad-line LINER. Our MMT longslit observation indicates that the kinematics of the extended Hα emission is consistent with a rotational gaseous disk, with a mean blueshifted velocity of 162 km s$^{-1}$ and mean redshifted velocity of 86 km s$^{-1}$ . According to our photoionization calculations, the large-scale Hα emission is unlikely to be powered by the central nucleus or by hot evolved (post-AGB) stars interspersed in the old stellar populations, but by in situ star formation; this is vindicated by the line-ratio diagnostic of the extended emission. We propose that both the ring and large-scale Hα-emitting gas are created by the tidal accretion in a collision-and then merger-with a gas-rich galaxy of a comparable mass.

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arXiv2017

Cosmic Galaxy-IGM HI Relation at ${\it{z}}\sim 2-3$ Probed in the COSMOS/UltraVISTA $1.6$ deg$^2$ Field

We present spatial correlations of galaxies and IGM HI in the COSMOS/UltraVISTA 1.62 deg$^2$ field. Our data consist of 13,415 photo-$z$ galaxies at $z\sim2-3$ with $K_s<23.4$ and the Ly$α$ forest absorptions in the background quasar spectra selected from SDSS data with no signature of damped Ly$α$ system contamination. We estimate a galaxy overdensity $δ_{gal}$ in an impact parameter of 2.5 pMpc, and calculate the Ly$α$ forest fluctuations $δ_{\langle F\rangle}$ whose negative values correspond to the strong Ly$α$ forest absorptions. We identify weak evidence of an anti-correlation between $δ_{gal}$ and $δ_{\langle F\rangle}$ with a Spearman's rank correlation coefficient of $-0.39$ suggesting that the galaxy overdensities and the Ly$α$ forest absorptions positively correlate in space at the $\sim90\%$ confidence level. This positive correlation indicates that high-$z$ galaxies exist around an excess of HI gas in the Ly$α$ forest. We find four cosmic volumes, dubbed $A_{obs}$-$D_{obs}$, that have extremely large (small) values of $δ_{gal} \simeq0.8$ ($-1$) and $δ_{\langle F\rangle}$ $\simeq0.1$ ($-0.4$), three out of which, $B_{obs}$-$D_{obs}$, significantly depart from the correlation, and weaken the correlation signal. We perform cosmological hydrodynamical simulations, and compare with our observational results. Our simulations reproduce the correlation, agreeing with the observational results. Moreover, our simulations have model counterparts of $A_{obs}$-$D_{obs}$, and suggest that the observations pinpoint, by chance, a galaxy overdensity like a proto-cluster, gas filaments lying on the sightline, a large void, and orthogonal low-density filaments. Our simulations indicate that the significant departures of $B_{obs}$-$D_{obs}$ are produced by the filamentary large-scale structures and the observation sightline effects.

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arXiv2016

MApping the Most Massive Overdensities (MAMMOTH) II -- Discovery of an Extremely Massive Overdensity BOSS1441 at $z=2.32$

Cosmological simulations suggest a strong correlation between high optical-depth Ly$α$ absorbers, which arise from the intergalactic medium (IGM), and 3-D mass overdensities on scales of $10-30$ $h^{-1}$ comoving Mpc. By examining the absorption spectra of $\sim$ 80,000 QSO sight-lines over a volume of 0.1 Gpc$^3$ in the Sloan Digital Sky Survey III (SDSS-III), we have identified an extreme overdensity, BOSS1441, which contains a rare group of strong Ly$α$ absorbers at $z=2.32\pm 0.02$. This absorber group is associated with six QSOs at the same redshift on a 30 comoving Mpc scale. Using Mayall/MOSAIC narrowband and broadband imaging, we detect Ly$α$ emitters (LAEs) down to $0.7\times L_{\rm{Lyα}}^*$, and reveal a large-scale structure of Ly$α$ emitters (LAEs) in this field. Our follow-up Large Binocular Telescope (LBT) observations have spectroscopically confirmed 19 galaxies in the density peak. We show that BOSS1441 has an LAE overdensity of $10.8\pm 2.6$ on a 15 comoving Mpc scale which could collapse to a massive cluster with $M\gtrsim10^{15}$ M$_\odot$ at $z\sim0$. This overdensity is among the most massive large-scale structures at $z\sim2$ discovered to date.

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arXiv2016

Lyman-Alpha Emitter Galaxies at z ~ 2.8 in the Extended Chandra Deep Field-South: I. Tracing the Large-Scale Structure via Lyman-Alpha Imaging

We present a narrowband survey with three adjacent filters for z=2.8--2.9 Lyman Alpha Emitter (LAE) galaxies in the Extended Chandra Deep Field South (ECDFS), along with spectroscopic followup. With a complete sample of 96 LAEs in the narrowband NB466, we confirm a large-scale structure at z~ 2.8. Compared to the blank field in NB470 and NB475, the LAE density excess in the NB466 field is ~6.0+/-0.8 times the standard deviation expected at z~2.8, assuming a linear bias of 2. The overdense large scale structure in NB466 can be decomposed into 4 protoclusters, whose overdensities are 4.6 - 6.6. These 4 protoclusters are expected to evolve into a Coma-like cluster at z~ 0. In the meanwhile, we investigate the average star-formation rates derived from Lyα, rest-frame UV and X-ray, the Lyα luminosity functions, the Lyα photon densities and their dependence on the environment. We find that the Lyα photon density in the overdense field (NB466) is ~50\% higher than that in the blank field (NB470+NB475). The 3 brightest LAEs, including a quasar at z=2.81, are all detected in X-ray and in NB466. These three LAE-AGNs contribute an extra 20--30\% Lyα photon density. Furthermore, we find that LAEs in overdense regions are younger and less dusty. We conclude that the structure we found is a significant and rare density peak, and narrowband imaging is an efficient method to detect and study such structures in the high-z universe.

astro-ph.CO↗

arXiv2016

A survey of luminous high-redshift quasars with SDSS and WISE. I. target selection and optical spectroscopy

High-redshift quasars are important tracers of structure and evolution in the early universe. However, they are very rare and difficult to find when using color selection because of contamination from late-type dwarfs. High-redshift quasar surveys based on only optical colors suffer from incompleteness and low identification efficiency, especially at $z\gtrsim4.5$. We have developed a new method to select $4.7\lesssim z \lesssim 5.4$ quasars with both high efficiency and completeness by combining optical and mid-IR Wide-field Infrared Survey Explorer (WISE) photometric data, and are conducting a luminous $z\sim5$ quasar survey in the whole Sloan Digital Sky Survey (SDSS) footprint. We have spectroscopically observed 99 out of 110 candidates with $z$-band magnitudes brighter than 19.5 and 64 (64.6\%) of them are quasars with redshifts of $4.4\lesssim z \lesssim 5.5$ and absolute magnitudes of $-29\lesssim M_{1450} \lesssim -26.4$. In addition, we also observed 14 fainter candidates selected with the same criteria and identified 8 (57.1\%) of them as quasars with $4.7 4.5$, which will set strong constraints on the bright end of the quasar luminosity function. We also expand our method to select quasars at $z\gtrsim5.7$. In this paper we report the discovery of four new luminous $z\gtrsim5.7$ quasars based on SDSS-WISE selection.

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arXiv2016

The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Overview and Early Data

The Extended Baryon Oscillation Spectroscopic Survey (eBOSS) will conduct novel cosmological observations using the BOSS spectrograph at Apache Point Observatory. Observations will be simultaneous with the Time Domain Spectroscopic Survey (TDSS) designed for variability studies and the Spectroscopic Identification of eROSITA Sources (SPIDERS) program designed for studies of X-ray sources. eBOSS will use four different tracers to measure the distance-redshift relation with baryon acoustic oscillations (BAO). Using more than 250,000 new, spectroscopically confirmed luminous red galaxies at a median redshift z=0.72, we project that eBOSS will yield measurements of $d_A(z)$ to an accuracy of 1.2% and measurements of H(z) to 2.1% when combined with the z>0.6 sample of BOSS galaxies. With ~195,000 new emission line galaxy redshifts, we expect BAO measurements of $d_A(z)$ to an accuracy of 3.1% and H(z) to 4.7% at an effective redshift of z= 0.87. A sample of more than 500,000 spectroscopically-confirmed quasars will provide the first BAO distance measurements over the redshift range 0.9 2.1; these new data will enhance the precision of $d_A(z)$ and H(z) by a factor of 1.44 relative to BOSS. Furthermore, eBOSS will provide improved tests of General Relativity on cosmological scales through redshift-space distortion measurements, improved tests for non-Gaussianity in the primordial density field, and new constraints on the summed mass of all neutrino species. Here, we provide an overview of the cosmological goals, spectroscopic target sample, demonstration of spectral quality from early data, and projected cosmological constraints from eBOSS.

astro-ph.CO↗

arXiv2015

MApping the Most Massive Overdensities Through Hydrogen (MAMMOTH) I: Methodology

Modern cosmology predicts that a galaxy overdensity is associated to a large reservoir of the intergalactic gas, which can be traced by the Ly$α$ forest absorption. We have undertaken a systematic study of the relation between Coherently Strong intergalactic Ly$α$ Absorption systems (CoSLAs), which have highest optical depth ($τ$) in $τ$ distribution, and mass overdensities on the scales of $\sim$ 10 - 20 $h^{-1}$ comoving Mpc. On such large scales, our cosmological simulations show a strong correlation between the effective optical depth ($τ_{\rm{eff}}$) of the CoSLAs and the 3-D mass overdensities. In moderate signal-to-noise spectra, however, the profiles of CoSLAs can be confused with high column density absorbers. For $z>2.6$, where the corresponding Ly$β$ is redshifted to the optical, we have developed the technique to differentiate between these two alternatives. We have applied this technique to SDSS-III quasar survey at $z = 2.6$ - 3.3, and we present a sample of five CoSLA candidates with $τ_{\rm{eff}}$ on 15 $h^{-1}$ Mpc greater than $4.5\times$ the mean optical depth. At lower redshifts of $z < 2.6$, where the background quasar density is higher, the overdensity can be traced by intergalactic absorption groups using multiple sight lines. Our overdensity searches fully utilize the current and next generation of Ly$α$ forest surveys which cover a survey volume of $> (1\ h^{-1}$ Gpc)$^3$. In addition, systems traced by CoSLAs will build a uniform sample of the most massive overdensities at $z > 2$ to constrain the models of structure formation, and offer a unique laboratory to study the interactions between galaxy overdensities and the intergalactic medium.

astro-ph.GA↗

arXiv2015

The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Quasar Target Selection

As part of the Sloan Digital Sky Survey IV the extended Baryon Oscillation Spectroscopic Survey (eBOSS) will improve measurements of the cosmological distance scale by applying the Baryon Acoustic Oscillation (BAO) method to quasar samples. eBOSS will adopt two approaches to target quasars over 7500 sq. deg. First, a "CORE" quasar sample will combine optical selection in ugriz using a likelihood-based routine called XDQSOz, with a mid-IR-optical color-cut. eBOSS CORE selection (to g < 22 OR r < 22) should return ~ 70 quasars per sq. deg. at redshifts 0.9 < z < 2.2 and ~7 z > 2.1 quasars per sq. deg. Second, a selection based on variability in multi-epoch imaging from the Palomar Transient Factory should recover an additional ~3-4 z > 2.1 quasars per sq. deg. to g < 22.5. A linear model of how imaging systematics affect target density recovers the angular distribution of eBOSS CORE quasars over 96.7% (76.7%) of the SDSS North (South) Galactic Cap area. The eBOSS CORE quasar sample should thus be sufficiently dense and homogeneous over 0.9 < z < 2.2 to yield the first few-percent-level BAO constraint near z~1.5. eBOSS quasars at z > 2.1 will be used to improve BAO measurements in the Lyman-alpha Forest. Beyond its key cosmological goals, eBOSS should be the next-generation quasar survey, comprising > 500,000 new quasars and > 500,000 uniformly selected spectroscopically confirmed 0.9 < z < 2.2 quasars. At the conclusion of eBOSS, the SDSS will have provided unique spectra of over 800,000 quasars.

astro-ph.CO↗

arXiv2015

An ultra-luminous quasar at z=5.363 with a ten billion solar mass black hole and a Metal-Rich DLA at z~5

We report the discovery of an ultra-luminous quasar J030642.51+185315.8 (hereafter J0306+1853) at redshift 5.363, which hosts a super-massive black hole (SMBH) with $M_{BH} = (1.07 \pm 0.27) \times10^{10}~M_\odot$. With an absolute magnitude $M_{1450}=-28.92$ and bolometric luminosity $L_{bol}\sim3.4\times10^{14} L_{\odot}$, J0306+1853 is one of the most luminous objects in the early Universe. It is not likely to be a beamed source based on its small flux variability, low radio loudness and normal broad emission lines. In addition, a $z=4.986$ Damped Ly$α$ system (DLA) with $\rm [M/H]=-1.3\pm0.1$, among the most metal rich DLAs at $z \gtrsim 5$, is detected in the absorption spectrum of this quasar. This ultra-luminous quasar puts strong constraint on the bright-end of quasar luminosity function and massive-end of black hole mass function. It will provide a unique laboratory to the study of BH growth and the co-evolution between BH and host galaxy with multi-wavelength follow-up observations. The future high resolution spectra will give more insights to the DLA and other absorption systems along the line-of-sight of J0306+1853.

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arXiv2015

Video (GIF) Sentiment Analysis using Large-Scale Mid-Level Ontology

With faster connection speed, Internet users are now making social network a huge reservoir of texts, images and video clips (GIF). Sentiment analysis for such online platform can be used to predict political elections, evaluates economic indicators and so on. However, GIF sentiment analysis is quite challenging, not only because it hinges on spatio-temporal visual contentabstraction, but also for the relationship between such abstraction and final sentiment remains unknown.In this paper, we dedicated to find out such relationship.We proposed a SentiPairSequence basedspatiotemporal visual sentiment ontology, which forms the midlevel representations for GIFsentiment. The establishment process of SentiPair contains two steps. First, we construct the Synset Forest to define the semantic tree structure of visual sentiment label elements. Then, through theSynset Forest, we organically select and combine sentiment label elements to form a mid-level visual sentiment representation. Our experiments indicate that SentiPair outperforms other competing mid-level attributes. Using SentiPair, our analysis frameworkcan achieve satisfying prediction accuracy (72.6%). We also opened ourdataset (GSO-2015) to the research community. GSO-2015 contains more than 6,000 manually annotated GIFs out of more than 40,000 candidates. Each is labeled with both sentiment and SentiPair Sequence.

cs.MM↗

arXiv2015

The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III

The third generation of the Sloan Digital Sky Survey (SDSS-III) took data from 2008 to 2014 using the original SDSS wide-field imager, the original and an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared high-resolution spectrograph, and a novel optical interferometer. All the data from SDSS-III are now made public. In particular, this paper describes Data Release 11 (DR11) including all data acquired through 2013 July, and Data Release 12 (DR12) adding data acquired through 2014 July (including all data included in previous data releases), marking the end of SDSS-III observing. Relative to our previous public release (DR10), DR12 adds one million new spectra of galaxies and quasars from the Baryon Oscillation Spectroscopic Survey (BOSS) over an additional 3000 sq. deg of sky, more than triples the number of H-band spectra of stars as part of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE), and includes repeated accurate radial velocity measurements of 5500 stars from the Multi-Object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The APOGEE outputs now include measured abundances of 15 different elements for each star. In total, SDSS-III added 2350 sq. deg of ugriz imaging; 155,520 spectra of 138,099 stars as part of the Sloan Exploration of Galactic Understanding and Evolution 2 (SEGUE-2) survey; 2,497,484 BOSS spectra of 1,372,737 galaxies, 294,512 quasars, and 247,216 stars over 9376 sq. deg; 618,080 APOGEE spectra of 156,593 stars; and 197,040 MARVELS spectra of 5,513 stars. Since its first light in 1998, SDSS has imaged over 1/3 of the Celestial sphere in five bands and obtained over five million astronomical spectra.

astro-ph.IM↗

arXiv2015

Discovery of Eight z ~ 6 Quasars in the Sloan Digital Sky Survey Overlap Regions

We present the discovery of eight quasars at z~6 identified in the Sloan Digital Sky Survey (SDSS) overlap regions. Individual SDSS imaging runs have some overlap with each other, leading to repeat observations over an area spanning >4000 deg^2 (more than 1/4 of the total footprint). These overlap regions provide a unique dataset that allows us to select high-redshift quasars more than 0.5 mag fainter in the z band than those found with the SDSS single-epoch data. Our quasar candidates were first selected as i-band dropout objects in the SDSS imaging database. We then carried out a series of follow-up observations in the optical and near-IR to improve photometry, remove contaminants, and identify quasars. The eight quasars reported here were discovered in a pilot study utilizing the overlap regions at high galactic latitude (|b|>30 deg). These quasars span a redshift range of 5.86<z<6.06 and a flux range of 19.3<z_AB<20.6 mag. Five of them are fainter than z_AB=20 mag, the typical magnitude limit of z~6 quasars used for the SDSS single-epoch images. In addition, we recover eight previously known quasars at z~6 that are located in the overlap regions. These results validate our procedure for selecting quasar candidates from the overlap regions and confirming them with follow-up observations, and provide guidance to a future systematic survey over all SDSS imaging regions with repeat observations.

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arXiv2014

Constraining Very High Mass Population III Stars through He II Emission in Galaxy BDF-521 at z = 7.01

Numerous theoretical models have long proposed that a strong He II 1640 emission line is the most prominent and unique feature of massive Population III (Pop III) stars in high redshift galaxies. The He II 1640 line strength can constrain the mass and IMF of Pop III stars. We use F132N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) to look for strong He II lambda 1640 emission in the galaxy BDF-521 at z=7.01, one of the most distant spectroscopically-confirmed galaxies to date. Using deep F132N narrowband imaging, together with our broadband imaging with F125W and F160W filters, we do not detect He II emission from this galaxy, but place a 2-sigma upper limit on the flux of 5.3x10^-19 ergs s^-1 cm^-2. This measurement corresponds to a 2-sigma upper limit on the Pop III star formation rate (SFR_PopIII) of ~ 0.2 M_solar yr^-1, assuming a Salpeter IMF with 50< M/M_solar < 1000. From the high signal-to-noise broadband measurements in F125W and F160W, we fit the UV continuum for BDF-521. The spectral flux density is ~ 3.6x 10^-11 lambda^-2.32 ergs s^-1 cm^-2 A^-1, which corresponds to an overall unobscured SFR of ~ 5 M_solar yr^-1. Our upper limit on SFR_PopIII suggests that massive Pop III stars represent < 4% of the total star formation. Further, the HST high resolution imaging suggests that BDF-521 is an extremely compact galaxy, with a half-light radius of 0.6 kpc.

astro-ph.GA↗

arXiv2014

A Glimpse at Quasar Host Galaxy Far-UV Emission, Using DLAs as Natural Coronagraphs

In merger-driven models of massive galaxy evolution, the luminous quasar phase is expected to be accompanied by vigorous star formation in quasar host galaxies. In this paper, we use high column density Damped Lyman Alpha (DLA) systems along quasar sight lines as natural coronagraphs to directly study the far-UV (FUV) radiation from the host galaxies of luminous background quasars. We have stacked the spectra of $\sim$2,000 DLA systems (N_HI>10^{20.6} cm^{-2}) with a median absorption redshift < z > = 2.6 selected from quasars observed in the SDSS-III Baryon Oscillation Spectroscopic Survey. We detect residual flux in the dark troughs of the composite DLA spectra. The level of this residual flux significantly exceeds systematic errors in the SDSS fiber sky subtraction; furthermore, the residual flux is strongly correlated with the continuum luminosity of the background quasar, while uncorrelated with DLA column density or metallicity. We conclude that the flux could be associated with the average FUV radiation from the background quasar host galaxies (with medium redshift < z > = 3.1) that is not blocked by the intervening DLA. Assuming all of the detected flux originates from quasar hosts, for the highest quasar luminosity bin (< L >= 2.5x 10^{13} L_sun), the host galaxy has a FUV intensity of 1.5 +/- 0.2 x 10^{40} erg s^{-1} A^{-1}; this corresponds to an unobscured UV star formation rate of 9 M_sun/yr.

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