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تسجيل مستخدم جديدSubaru Deep Spectroscopy of a Star-forming Companion Galaxy of BR 1202-0725 at $z=4.7$
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We present deep spatially-resolved optical spectroscopy of the NW companion galaxy of the quasar BR 1202-0725 at $z=4.7$. Its rest-frame UV spectrum shows star-forming activity in the nuclear region. The Ly$alpha$ emission profile is symmetric with wavelength while its line width is unusually wide (FWHM $simeq 1100$ km s$^{-1}$) for such a high-$z$ star-forming galaxy. Spectrum taken along the Ly$alpha$ nebula elongation, which is almost along the minor axis of the companion host galaxy, reveals that off-nuclear Ly$alpha$ nebulae have either flat-topped or multi-peaked profiles along the extension. All these properties can be understood in terms of superwind activity in the companion galaxy. We also find a diffuse continuum component around the companion, which shows similar morphology to that of Ly$alpha$ nebula, and is most likely due to scattering of the quasar light at dusty halo around the companion. We argue that the superwind could expel dusty material out to the halo region, making a dusty halo for scattering.
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The radio-quiet quasar BR1202-0725 (z=4.695) is a remarkable source with a bright Northwest (NW) companion detected at submm and radio wavelengths but invisible in the optical. In the absence of amplification by gravitational lensing, BR1202-0725 wou
ld be the most luminous binary CO and FIR source in the Universe. In this paper, we report observations with the IRAM Plateau de Bure interferometer of BR1202-0725 in the redshifted emission of the CO(5-4) and (7-6) lines, the [C I](3P2-3P1) line, a high angular resolution (0.3 x 0.8 arcsec) 1.3 mm map of the rest-frame, far-IR dust continuum, and a search for the CO(11-10) line. We compare these results with recent ALMA data in the [C II] line. Both the quasar host galaxy and its NW companion are spatially resolved in the molecular line emission and the dust continuum. The CO profile of the NW companion is very broad with a full width at half maximum of 1000 +/- 130 km/s, compared to 360 +/- 40 km/s for the quasar host galaxy to the Southeast (SE). The difference in linewidths and center velocities, and the absence of any lens candidate or arc-like structure in the field, at any wavelength, show that the obscured NW galaxy and the SE quasar host galaxy cannot be lensed images of the same object. Instead, we find morphological and kinematic evidence for sub-structures in both the NW and SE sources. We interpret these results as strong indications that the BR1202-0725 complex is a group of young, interacting, and highly active starburst galaxies.
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 D
eep Field. This field has reliable ({Delta}z/(1 + z) = 0.02--0.09) photometric redshifts for ~53,000 galaxies from 20 bands (1500{AA}--2.2{mu}m). 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.
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