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Register a new userA new Einstein Cross gravitational lens of a Lyman-break galaxy
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D. Bettoni
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We report the study of an Einstein Cross configuration first identified in a set of HST images by Cerny et al. 2018. Deep spectroscopic observations obtained at the Spanish 10.4m GTC telescope, allowed us to demonstrate the lens nature of the system, that consists of a Lyman-break galaxy, not a QSO as is usually the case, at z = 3.03 lensed by a galaxy at z=0.556. Combining the new spectroscopy with the archival HST data, it turns out that the lens is an elliptical galaxy with M_V =-21.0, effective radius 2.8 kpc and stellar velocity dispersion sigma=208+-39 km/sec. The source is a Lyman break galaxy with Ly_alpha luminosity ~L* at that redshift. From the modeling of the system, performed by assuming a singular isothermal ellipsoid (SIE) with external shear, we estimate that the flux source is magnified about 4.5 times, and the velocity dispersion of the lens is sigma_SIE=197.9-1.3+2.6 km/s, in good agreement with the value derived spectroscopically. This is the second case known of an Einstein cross of a Lyman-break galaxy.
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We report the serendipitous discovery of a quadruply-lensed source behind the z=0.095 edge-on disk galaxy 2MASXJ13170000-1405187, based on public imaging survey data from Pan-STARRS PS1 and the VISTA Hemisphere Survey. Follow-up imaging from Magellan/LDSS3 shows that the background source is spatially extended (i.e. not a QSO), and that two of the lensed images are observed through a prominent dust ring in the disk of the lens galaxy. We summarise results of preliminary modelling, which indicates an Einstein radius of 1.44 arcsec, and a K-band mass-to-light ratio of 0.5, relative to the solar value.
We present VLT/SINFONI near-infrared (NIR) integral field spectroscopy of six $z sim 0.2$ Lyman break galaxy analogs (LBAs), from which we detect HI, HeI, and [FeII] recombination lines, and multiple H$_2$ ro-vibrational lines in emission. Pa$alpha$ kinematics reveal high velocity dispersions and low rotational velocities relative to random motions ($langle v/sigma rangle = 1.2 pm 0.8$). Matched-aperture comparisons of H$beta$, H$alpha$, and Pa$alpha$ reveal that the nebular color excesses are lower relative to the continuum color excesses than is the case for typical local star-forming systems. We compare observed HeI/HI recombination line ratios to photoionization models to gauge the effective temperatures (T$_{rm eff}$) of massive ionizing stars, finding the properties of at least one LBA are consistent with extra heating from an active galactic nucleus (AGN) and/or an overabundance of massive stars. We use H$_2$ 1-0 S($cdot$) ro-vibrational spectra to determine rotational excitation temperature $T_{rm ex} sim 2000$ K for warm molecular gas, which we attribute to UV heating in dense photon-dominated regions. Spatially resolved NIR line ratios favor excitation by massive, young stars, rather than supernovae or AGN feedback. Our results suggest that the local analogs of Lyman break galaxies are primarily subject to strong feedback from recent star formation, with evidence for AGN and outflows in some cases.
We present a spectroscopic redshift measurement of a very bright Lyman break galaxy at z=7.7302+-0.0006 using Keck/MOSFIRE. The source was pre-selected photometrically in the EGS field as a robust z~8 candidate with H=25.0 mag based on optical non-detections and a very red Spitzer/IRAC [3.6]-[4.5] broad-band color driven by high equivalent width [OIII]+Hbeta line emission. The Lyalpha line is reliably detected at 6.1 sigma and shows an asymmetric profile as expected for a galaxy embedded in a relatively neutral inter-galactic medium near the Planck peak of cosmic reionization. The line has a rest-frame equivalent width of EW0=21+-4 A and is extended with V_FWHM=360+90-70 km/s. The source is perhaps the brightest and most massive z~8 Lyman break galaxy in the full CANDELS and BoRG/HIPPIES surveys, having assembled already 10^(9.9+-0.2) M_sol of stars at only 650 Myr after the Big Bang. The spectroscopic redshift measurement sets a new redshift record for galaxies. This enables reliable constraints on the stellar mass, star-formation rate, formation epoch, as well as combined [OIII]+Hbeta line equivalent widths. The redshift confirms that the IRAC [4.5] photometry is very likely dominated by line emission with EW0(OIII+Hbeta)= 720-150+180 A. This detection thus adds to the evidence that extreme rest-frame optical emission lines are a ubiquitous feature of early galaxies promising very efficient spectroscopic follow-up in the future with infrared spectroscopy using JWST and, later, ELTs.
We present new Atacama Large Millimeter/submillimeter Array Band 7 observational results of a Lyman break galaxy at $ z=7.15 $, B14-65666 (Big Three Dragons), which is an object detected in [OIII] 88 $rm{mu m}$, [CII] 158 $rm{mu m}$, and dust-continuum emission during the epoch of reionization. Our targets are the [NII] 122 $rm{mu m}$ fine-structure emission line and underlying 120 $rm{mu m}$ dust continuum. The dust continuum is detected with a $ sim $19$ sigma $ significance. From far-infrared spectral energy distribution sampled at 90, 120, and 160 $rm{mu m}$, we obtaine a best-fit dust temperature of $ 40 $ K ($ 79 $ K) and an infrared luminosity of $ log_{10}(L_{rm IR}/{rm L}_odot)=11.6$ ($12.1$) at the emissivity index $ beta = 2.0 $ (1.0). The [NII] 122 $rm{mu m}$ line is not detected. The 3$ sigma $ upper limit of the [NII] luminosity is $ 8.1 times 10^7 {rm L}_odot$. From the [NII], [OIII], and [CII] line luminosities, we use the Cloudy photoionization code to estimate nebular parameters as functions of metallicity. If the metallicity of the galaxy is high ($ Z > 0.4 {rm Z}_odot$), the ionization parameter and hydrogen density are $ log_{10} U simeq -2.7pm0.1$ and $ n_text{H} simeq 50$-$250 {rm cm}^{-3}$, respectively, which are comparable to those measured in low-redshift galaxies. The nitrogen-to-oxygen abundance ratio, $rm{N/O}$, is constrained to be sub-solar. At $ Z < 0.4 {rm Z}_odot$, the allowed $ U $ drastically increases as the assumed metallicity decreases. For high ionization parameters, the $rm{N/O}$ constraint becomes weak. Finally, our Cloudy models predict the location of B14-65666 on the BPT diagram, thereby allowing a comparison with low-redshift galaxies.
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