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Register a new userA highly magnified candidate for a young galaxy seen when the Universe was 500 Myrs old
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The early Universe at redshift zsim6-11 marks the reionization of the intergalactic medium, following the formation of the first generation of stars. However, those young galaxies at a cosmic age of lesssim 500 million years (Myr, at z gtrsim 10) remain largely unexplored as they are at or beyond the sensitivity limits of current large telescopes. Gravitational lensing by galaxy clusters enables the detection of high-redshift galaxies that are fainter than what otherwise could be found in the deepest images of the sky. We report the discovery of an object found in the multi-band observations of the cluster MACS1149+22 that has a high probability of being a gravitationally magnified object from the early universe. The object is firmly detected (12 sigma) in the two reddest bands of HST/WFC3, and not detected below 1.2 {mu}m, matching the characteristics of zsim9 objects. We derive a robust photometric redshift of z = 9.6 pm 0.2, corresponding to a cosmic age of 490 pm 15Myr (i.e., 3.6% of the age of the Universe). The large number of bands used to derive the redshift estimate make it one of the most accurate estimates ever obtained for such a distant object. The significant magnification by cluster lensing (a factor of sim15) allows us to analyze the objects ultra-violet and optical luminosity in its rest-frame, thus enabling us to constrain on its stellar mass, star-formation rate and age. If the galaxy is indeed at such a large redshift, then its age is less than 200 Myr (at the 95% confidence level), implying a formation redshift of zf lesssim 14. The object is the first z>9 candidate that is bright enough for detailed spectroscopic studies with JWST, demonstrating the unique potential of galaxy cluster fields for finding highly magnified, intrinsically faint galaxies at the highest redshifts.
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Galaxies evolve from a blue star-forming phase into a red quiescent one by quenching their star formation activity. In high density environments, this galaxy evolution proceeds earlier and more efficiently. Therefore, local galaxy clusters are dominated by well-evolved red, elliptical galaxies. The fraction of blue galaxies in clusters monotonically declines with decreasing redshift, i.e., the Butcher-Oemler effect. In the local Universe, observed blue fractions of massive clusters are as small as $lesssim$ 0.2. Here we report a discovery of a lq lq blue clusterrq rq, that is a local galaxy cluster with an unprecedentedly high fraction of blue star-forming galaxies yet hosted by a massive dark matter halo. The blue fraction is 0.57, which is 4.0 $sigma$ higher than those of the other comparison clusters under the same selection and identification criteria. The velocity dispersion of the member galaxies is 510 km s$^{-1}$, which corresponds to a dark matter halo mass of 2.0$^{+1.9}_{-1.0}times 10^{14}$ M$_{odot}$. The blue fraction of the cluster is more than 4.7 $sigma$ beyond the standard theoretical predictions including semi-analytic models of galaxy formation. The probability to find such a high blue fraction in an individual cluster is only 0.003%, which challenges the current standard frameworks of the galaxy formation and evolution in the $Lambda$CDM Universe. The spatial distribution of galaxies around the blue cluster suggests that filamentary cold gas streams can exist in massive halos even in the local Universe. However these cold streams have already disappeared in the theoretically simulated local universes.
We present new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of the [CII] 158 $mu$m transition and the dust continuum in HZ4, a typical star-forming galaxy when the Universe was only $sim1$ Gyr old ($zapprox5.5$). Our high $approx0.3$ spatial resolution allow us to study the relationships between [CII] line emission, star formation rate (SFR), and far-infrared (FIR) emission on spatial scales of $sim2$ kpc. In the central $sim$4 kpc of HZ4, the [CII]/FIR ratio is $sim3times10^{-3}$ on global scales as well as on spatially-resolved scales of $sim$2 kpc, comparable to the ratio observed in local moderate starburst galaxies such as M82 or M83. For the first time in an individual normal galaxy at this redshift, we find evidence for outflowing gas from the central star-forming region in the direction of the minor-axis of the galaxy. The projected velocity of the outflow is $sim400$ km s$^{-1}$, and the neutral gas mass outflow rate is $sim3-6$ times higher than the SFR in the central region. Finally, we detect a diffuse component of [CII] emission, or [CII]-halo, that extends beyond the star-forming disk and has a size of $sim12$ kpc in diameter. Most likely the outflow, which has a velocity approximately half the escape velocity of the system, is in part responsible for fueling the [CII] extended emission. Together with the kinematic analysis of HZ4 (presented in a forthcoming paper), the analysis supports that HZ4 is a typical star-forming disk at $zsim5$ with interstellar medium (ISM) conditions similar to present-day galaxies forming stars at a similar level, driving a galactic outflow that may already play a role in its evolution.
We present optical and near-IR imaging and spectroscopy of SGAS J105039.6$+$001730, a strongly lensed galaxy at z $=$ 3.6252 magnified by $>$30$times$, and derive its physical properties. We measure a stellar mass of log(M$_{*}$/M$_{odot}$) $=$ 9.5 $pm$ 0.35, star formation rates from [O II]$lambda$$lambda$3727 and H-$beta$ of 55 $pm$ 20 and 84 $pm$ 17 M$_{odot}$ yr$^{-1}$, respectively, an electron density of n$_{e} leq$ 10$^{3}$ cm$^{-2}$, an electron temperature of T$_{e} leq$ 14000 K, and a metallicity of 12+log(O/H) $=$ 8.3 $pm$ 0.1. The strong C III]$lambda$$lambda$1907,1909 emission and abundance ratios of C, N, O and Si are consistent with well-studied starbursts at z $sim$ 0 with similar metallicities. Strong P Cygni lines and He II$lambda$1640 emission indicate a significant population of Wolf-Rayet stars, but synthetic spectra of individual populations of young, hot stars do not reproduce the observed integrated P Cygni absorption features. The rest-frame UV spectral features are indicative of a young starburst with high ionization, implying either 1) an ionization parameter significantly higher than suggest by rest-frame optical nebular lines, or 2) differences in one or both of the initial mass function and the properties of ionizing spectra of massive stars. We argue that the observed features are likely the result of a superposition of star forming regions with different physical properties. These results demonstrate the complexity of star formation on scales smaller than individual galaxies, and highlight the importance of systematic effects that result from smearing together the signatures of individual star forming regions within galaxies.
We present a comprehensive analysis of the rest-frame UV to near-IR spectral energy distributions and rest-frame optical spectra of four of the brightest gravitationally lensed galaxies in the literature: RCSGA 032727-132609 at z=1.70, MS1512-cB58 at z=2.73, SGAS J152745.1+065219 at z=2.76 and SGAS J122651.3+215220 at z=2.92. This includes new Spitzer imaging for RCSGA0327 as well as new spectra, near-IR imaging and Spitzer imaging for SGAS1527 and SGAS1226. Lensing magnifications of 3-4 magnitudes allow a detailed study of the stellar populations and physical conditions. We compare star formation rates as measured from the SED fit, the H-alpha and [OII] emission lines, and the UV+IR bolometric luminosity where 24 micron photometry is available. The SFR estimate from the SED fit is consistently higher than the other indicators, which suggests that the Calzetti dust extinction law used in the SED fitting is too flat for young star-forming galaxies at z~2. Our analysis finds similar stellar population parameters for all four lensed galaxies: stellar masses 3-7*10^9 M_sun, young ages ~ 100 Myr, little dust content E(B-V)=0.10-0.25, and star formation rates around 20-100 M_sun/yr. Compared to typical values for the galaxy population at z~2, this suggests we are looking at newly formed, starbursting systems that have only recently started the build-up of stellar mass. These results constitute the first detailed, uniform analysis of a sample of the growing number of strongly lensed galaxies known at z~2.
In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z=0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The clusters gravitational potential also creates multiple images of the z=1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.
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