Marc Rafelski

University of California, Santa Barbara, Santa Barbara, California, United States

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Publications (39)143.39 Total impact

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    ABSTRACT: Although giant clumps of stars are crucial to galaxy formation and evolution, the most basic demographics of clumps are still uncertain, mainly because the definition of clumps has not been thoroughly discussed. In this paper, we study the basic demographics of clumps in star-forming galaxies (SFGs) at 0.5<z<3, using our proposed physical definition that UV-bright clumps are discrete star-forming regions that individually contribute more than 8% of the rest-frame UV light of their galaxies. Clumps defined this way are significantly brighter than the HII regions of nearby large spiral galaxies, either individually or blended, when physical spatial resolution and cosmological dimming are considered. Under this definition, we measure the fraction of SFGs that contain at least one off-center clump (Fclumpy) and the contributions of clumps to the rest-frame UV light and star formation rate of SFGs in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample consists of 3239 galaxies with axial ratio q>0.5. The redshift evolution of Fclumpy changes with the stellar mass (M*) of the galaxies. Low-mass (log(M*/Msun)<9.8) galaxies keep an almost constant Fclumpy of about 60% from z~3.0 to z~0.5. Intermediate-mass and massive galaxies drop their Fclumpy from 55% at z~3.0 to 40% and 15%, respectively, at z~0.5. We find that (1) the trend of disk stabilization predicted by violent disk instability matches the Fclumpy trend of massive galaxies; (2) minor mergers are a viable explanation of the Fclumpy trend of intermediate-mass galaxies at z<1.5, given a realistic observability timescale; and (3) major mergers are unlikely responsible for the Fclumpy trend in all masses at z<1.5. The clump contribution to the rest-frame UV light of SFGs shows a broad peak around galaxies with log(M*/Msun)~10.5 at all redshifts, possibly linked to the molecular gas fraction of the galaxies. (Abridged)
    10/2014;
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    ABSTRACT: We present a robust measurement and analysis of the rest-frame ultraviolet (UV) luminosity function at z=4-8. We use deep Hubble Space Telescope imaging over the CANDELS/GOODS fields, the Hubble Ultra Deep Field and the Year 1 Hubble Frontier Field deep parallel observations. These surveys provides an effective volume of 0.6-1.2 x 10^6 Mpc^3 over this epoch, allowing us to perform a robust search for bright (M_UV < -21) and faint (M_UV=-18) galaxies. We select galaxies using a well-tested photometric redshift technique with careful screening of contaminants, finding a sample of 7446 galaxies at 3.5<z<8.5, with >1000 galaxies at z~6-8. We measure the luminosity function using a Markov Chain Monte Carlo analysis to measure robust uncertainties. At the faint end our results agree with previous studies, yet we find a higher abundance of UV-bright galaxies at z>6, with M* ~ -21 at z>5, different than that inferred based on previous trends at lower redshift. At z=8, a single power-law provides an equally good fit to the UV luminosity function, while at z=6 and 7, an exponential cutoff at the bright-end is moderately preferred. We compare to semi-analytical models, and find that the lack of evolution in M* is consistent with models where the impact of dust attenuation on the bright-end of the luminosity function decreases at higher redshift. We measure the evolution of the cosmic star-formation rate density, correcting for dust attenuation, and find that it declines as (1+z)^(-4.3 +/- 0.5) at z>4, consistent with observations at z>9. Our observations are consistent with a reionization history that starts at z>10, completes at z>6, and reaches a midpoint (x_HII = 0.5) at 6.7<z<9.4. Finally, our observations predict that the abundance of bright z=9 galaxies is likely higher than previous constraints, though consistent with recent estimates of bright z~10 galaxies. [abridged]
    10/2014;
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    ABSTRACT: We study the relationship between the structure and star-formation rate (SFR) of X-ray selected low and moderate luminosity active galactic nuclei (AGNs) in the two Chandra Deep Fields, using Hubble Space Telescope imaging from the Cosmic Assembly Near Infrared Extragalactic Legacy Survey (CANDELS) and deep far-infrared maps from the PEP+GOODS-Herschel survey. We derive detailed distributions of structural parameters and FIR luminosities from carefully constructed control samples of galaxies, which we then compare to those of the AGNs. At z~1, AGNs show slightly diskier light profiles than massive inactive (non-AGN) galaxies, as well as modestly higher levels of gross galaxy disturbance (as measured by visual signatures of interactions and clumpy structure). In contrast, at z~2, AGNs show similar levels of galaxy disturbance as inactive galaxies, but display a red central light enhancement, which may arise due to a more pronounced bulge in AGN hosts or due to extinguished nuclear light. We undertake a number of tests of these alternatives, but our results do not strongly favour one interpretation over the other. The mean SFR and its distribution among AGNs and inactive galaxies are similar at z>1.5. At z<1, however, clear and significant enhancements are seen in the SFRs of AGNs with bulge-dominated light profiles. These trends suggest an evolution in the relation between nuclear activity and host properties with redshift, towards a minor role for mergers and interactions at z>1.5.
    09/2014;
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    ABSTRACT: We present results from a survey designed to probe the star formation properties of 32 damped Ly-alpha systems (DLAs) at z~2.7. By using the "double-DLA" technique that eliminates the glare of the bright background quasars, we directly measure the rest-frame FUV flux from DLAs and their neighbouring galaxies. We place stringent constraints on the star formation rates (SFRs) of DLAs to 2-sigma limits of <0.09-0.27 M/yr, corresponding to SFR surface densities < 10^(-2.6)-10^(-1.5) M/yr/kpc^2. The implications of these limits for the star formation law, metal enrichment, and cooling rates of DLAs are examined. By studying the distribution of impact parameters as a function of SFRs for all the galaxies detected around these DLAs, we place new direct constraints on the bright end of the UV luminosity function of DLA hosts. We find that <13% of the hosts have SFR > 2 M/yr at impact parameters b < SFR^(0.8)+6 kpc, in contrast with current samples of confirmed DLA galaxies, which appear to be biased. Our observations also disfavor a scenario in which the majority of DLAs arise from bright LBGs at distances 20 < b < 100 kpc. These new findings corroborate a picture in which DLAs do not originate from highly star forming systems that are coincident with the absorbers, and instead suggest that DLAs are associated with faint, possibly isolated, star-forming galaxies. Potential shortcomings of this scenario and future strategies for further investigation are discussed.
    09/2014;
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    ABSTRACT: We present the largest, publicly available, sample of Damped Lyman-$\alpha$ systems (DLAs) along Gamma-ray Bursts (GRB) line of sights in order to investigate the environmental properties of long GRBs in the $z=1.8-6$ redshift range. Compared with the most recent quasar DLAs sample (QSO-DLA), our analysis shows that GRB-DLAs probe a more metal enriched environment at $z\gtrsim3$, up to $[X/H]\sim-0.5$. In the $z=2-3$ redshift range, despite the large number of lower limits, there are hints that the two populations may be more similar (only at 90\% significance level). Also at \hiz, the GRB-DLA average metallicity seems to decline at a shallower rate than the QSO-DLAs: GRB-DLA hosts may be polluted with metals at least as far as $\sim 2$kpc from the GRB explosion site, probably due to previous star-formation episodes and/or supernovae explosions. This shallow metallicity trend, extended now up to $z\sim5$, confirms previous results that GRB hosts are star-forming and have, on average, higher metallicity than the general QSO-DLA population. Finally, our metallicity measurements are broadly consistent with the hypothesis of two channels of GRB progenitors, one of which is mildly affected by a metallicity bias. The metallicity evolution of modeled GRB hosts agrees reasonably well with our data up to intermediate redshift, while more data are needed to constrain the models at $z\gtrsim 4$.
    08/2014;
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    ABSTRACT: We present the rest-frame UV wavelength dependence of the Petrosian-like half-light radius (r 50), and the concentration parameter for a sample of 198 star-forming galaxies at 0.5 < z < 1.5. We find a ~5% decrease in r 50 from 1500 Å to 3000 Å, with half-light radii at 3000 Å ranging from 0.6 kpc to 6 kpc. We also find a decrease in concentration of ~0.07 (1.9 < C 3000 < 3.9). The lack of a strong relationship between r 50 and wavelength is consistent with a model in which clumpy star formation is distributed over length scales comparable to the galaxy's rest-frame optical light. While the wavelength dependence of r 50 is independent of size at all redshifts, concentration decreases more sharply in the far-UV (~1500 Å) for large galaxies at z ~ 1. This decrease in concentration is caused by a flattening of the inner ~20% of the light profile in disk-like galaxies, indicating that the central regions have different UV colors than the rest of the galaxy. We interpret this as a bulge component with older stellar populations and/or more dust. The size-dependent decrease in concentration is less dramatic at z ~ 2, suggesting that bulges are less dusty, younger, and/or less massive than the rest of the galaxy at higher redshifts.
    The Astrophysical Journal 07/2014; 791(1):18. · 6.73 Impact Factor
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    ABSTRACT: We estimate the UV continuum slope, $\beta$, for 923 galaxies in the range $1 < z < 8$ in the Hubble Ultradeep Field (HUDF). These data include 460 galaxies at $1<z<2$ down to an absolute magnitude $M_{UV} = -14~(\sim 0.006~L^*_{z=1}; 0.02~L^*_{z=0}$), comparable to dwarf galaxies in the local universe. We combine deep HST/UVIS photometry in F225W, F275W, F336W wavebands (UVUDF) with recent data from HST/WFC3/IR (HUDF12). Galaxies in the range $1<z<2$ are significantly bluer than local dwarf galaxies. We find their mean (median) values $\left<\beta \right> = -1.382~(-1.830)\pm0.002$ (random) $\pm0.1$ (systematic). We find comparable scatter in $\beta$ (standard deviation = 0.43) to local dwarf galaxies and 30% larger scatter than $z>2$ galaxies. We study the trends of $\beta$ with redshift and absolute magnitude for binned sub-samples and find a modest color-magnitude relation, $d\beta/dM = -0.11 \pm 0.01$ and no evolution in $d\beta/dM$ with redshift. A modest increase in dust reddening with redshift and luminosity, $\Delta E(B-V) \sim 0.1$, and a comparable increase in the dispersion of dust reddening at $z<2$, appears likely to explain the observed trends. At $z>2$, we find trends that are consistent with previous works; combining our data with the literature in the range $1<z<8$, we find a color evolution with redshift, $d\beta/dz = -0.09\pm0.01$ for low luminosity (0.05 $L^*_{z=3}$), and $d\beta/dz = -0.06\pm0.01$ for medium luminosity (0.25 $L^*_{z=3}$) galaxies.
    The Astrophysical Journal Letters 07/2014; 793(1). · 6.35 Impact Factor
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    ABSTRACT: Near infrared slitless spectroscopy with the Wide Field Camera 3, on board the Hubble Space Telescope, offers a unique opportunity to study low-mass galaxy populations at high redshift (z ~ 1-2). While most high-z surveys are biased toward massive galaxies, we are able to select sources via their emission lines that have very faint continua. We investigate the star formation rate (SFR)-stellar mass (M ) relation for about 1000 emission line galaxies identified over a wide redshift range of 0.3 z 2.3. We use the Hα emission as an accurate SFR indicator and correct the broadband photometry for the strong nebular contribution to derive accurate stellar masses down to M ~107M ☉. We focus here on a subsample of galaxies that show extremely strong emission lines (EELGs) with rest-frame equivalent widths ranging from 200 to 1500 Å. This population consists of outliers to the normal SFR-M sequence with much higher specific SFRs (>10 Gyr–1). While on-sequence galaxies follow continuous star formation processes, EELGs are thought to be caught during an extreme burst of star formation that can double their stellar mass in a period of less than 100 Myr. The contribution of the starburst population to the total star formation density appears to be larger than what has been reported for more massive galaxies in previous studies. In the complete mass range 8.2 < log(M /M ☉) <10 and a SFR lower completeness limit of about 2 M ☉ yr–1 (10 M ☉ yr–1) at z ~ 1 (z ~ 2), we find that starbursts having EWrest(Hα) > 300, 200, and 100 Å contribute up to ~13%, 18%, and 34%, respectively, to the total SFR of emission-line-selected sample at z ~ 1-2. The comparison with samples of massive galaxies shows an increase in the contribution of starbursts toward lower masses.
    The Astrophysical Journal 06/2014; 789(2):96. · 6.73 Impact Factor
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    ABSTRACT: We present the discovery of two galaxy overdensities in the HST UDF: a proto-cluster, HUDFJ0332.4-2746.6 at $z = 1.84 \pm 0.01$, and a group, HUDFJ0332.5-2747.3 at $z =1.90 \pm 0.01$. The velocity dispersion of HUDFJ0332.4-2746.6 implies a mass of $M_{200}= (2.2 \pm 1.8) \times 10^{14} M_{\odot}$, consistent with the lack of extended X-ray emission. Neither overdensity shows evidence of a red sequence. About $50\%$ of their members show interactions and/or disturbed morphologies, which are a signature of merger remnants. Most of their morphologically classified ETGs have blue colors and show recent star-formation. These observations reveal for the first time large fractions of spectroscopically confirmed star-forming blue ETGs in proto-clusters at $z\approx 2$. These star-forming ETGs are most likely among the progenitors of the quiescent population in clusters at more recent epochs. Their mass-size relation is consistent with that of passive ETGs in clusters at $z\sim0.7-1.5$. If these galaxies are the progenitors of cluster ETGs at these lower redshifts, their size would evolve according to a similar mass-size relation. It is noteworthy that quiescent ETGs in clusters at $z=1.8-2$ also do not show any significant size evolution over this redshift range, contrary to field ETGs. The ETG fraction of our sample is $\lesssim 40\%$, compared to the typical quiescent ETG fraction of $\approx 80\%$ in cluster cores at $z< 1$. The fraction, masses and colors of the newly discovered ETGs imply that other cluster ETGs will be formed/accreted at later time.
    03/2014;
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    ABSTRACT: We present the rest-frame UV wavelength dependence of the Petrosian-like half-light radius ($r_{50}$), and the concentration parameter for a sample of 198 star-forming galaxies at 0.5 < z < 1.5. We find a ~5% decrease in $r_{50}$ from 1500 \AA\ to 3000 \AA, with half-light radii at 3000 \AA\ ranging from 0.6 kpc to 6 kpc. We also find a decrease in concentration of ~0.07 (1.9 < $C_{3000}$ < 3.9). The lack of a strong relationship between $r_{50}$ and wavelength is consistent with a model in which clumpy star formation is distributed over length scales comparable to the galaxy's rest-frame optical light. While the wavelength dependence of $r_{50}$ is independent of size at all redshifts, concentration decreases more sharply in the far-UV (~1500 \AA) for large galaxies at z ~ 1. This decrease in concentration is caused by a flattening of the inner ~20% of the light profile in disk-like galaxies, indicating that the central regions have different UV colors than the rest of the galaxy. We interpret this as a bulge component with older stellar populations and/or more dust. The size-dependent decrease in concentration is less dramatic at z ~ 2, suggesting that bulges are less dusty, younger, and/or less massive than the rest of the galaxy at higher redshifts.
    03/2014;
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    ABSTRACT: We present results from near-infrared spectroscopy of 26 emission-line galaxies at z ~ 2 obtained with the FIRE spectrometer on the Magellan Baade telescope. The sample was selected from the WISP survey, which uses the near-infrared grism of the Hubble Space Telescope Wide Field Camera 3 to detect emission-line galaxies over 0.3 < z < 2.3. Our FIRE follow-up spectroscopy (R~5000) over 1.0-2.5 micron permits detailed measurements of physical properties of the z~2 emission-line galaxies. Dust-corrected star formation rates for the sample range from ~5-100 M_sun yr-1. We derive a median metallicity for the sample of ~0.45 Z_sun, and the estimated stellar masses range from ~10^8.5 - 10^9.5 M_sun. The average ionization parameters measured for the sample are typically much higher than what is found for local star-forming galaxies. We derive composite spectra from the FIRE sample, from which we infer typical nebular electron densities of ~100-400 cm^-3. Based on the location of the galaxies and composite spectra on BPT diagrams, we do not find evidence for significant AGN activity in the sample. Most of the galaxies as well as the composites are offset in the BPT diagram toward higher [O III]/H-beta at a given [N II]/H-alpha, in agreement with other observations of z > 1 star-forming galaxies, but composite spectra derived from the sample do not show an appreciable offset from the local star-forming sequence on the [O III]/H-beta versus [S II]/H-alpha diagram. We infer a high nitrogen-to-oxygen abundance ratio from the composite spectrum, which may contribute to the offset of the high-redshift galaxies from the local star-forming sequence in the [O III]/H-beta versus [N II]/H-alpha diagram. We speculate that the elevated nitrogen abundance could result from substantial numbers of Wolf-Rayet stars in starbursting galaxies at z~2. (Abridged)
    The Astrophysical Journal 02/2014; 785(2):153. · 6.73 Impact Factor
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    ABSTRACT: We present evidence that the cosmological mean metallicity of neutral atomic hydrogen gas shows a sudden decrease at z > 4.7 down to \langle {Z}\rangle =-2.03^{+0.09}_{-0.11}, which is 6σ deviant from that predicted by a linear fit to the data at lower redshifts. This measurement is made possible by the chemical abundance measurements of eight new damped Lyα (DLA) systems at z > 4.7 observed with the Echellette Spectrograph and Imager on the Keck II Telescope, doubling the number of measurements at z > 4.7 to 16. Possible explanations for this sudden decrease in metallicity include a change in the physical processes that enrich the neutral gas within disks, or an increase of the covering factor of neutral gas outside disks due to a lower ultraviolet radiation field and higher density at high redshift. The later possibility would result in a new population of presumably lower metallicity DLAs, with an increased contribution to the DLA population at higher redshifts resulting in a reduced mean metallicity. Furthermore, we provide evidence of a possible decrease at z > 4.7 in the comoving metal mass density of DLAs, ρmetals(z)DLA, which is flat out to z ~ 4.3. Such a decrease is expected, as otherwise most of the metals from star-forming galaxies would reside in DLAs by z ~ 6. While the metallicity is decreasing at high redshift, the contribution of DLAs to the total metal budget of the universe increases with redshift, with DLAs at z ~ 4.3 accounting for ~20% as many metals as produced by Lyman break galaxies.
    The Astrophysical Journal Letters 01/2014; 782(2). · 6.35 Impact Factor
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    ABSTRACT: We present near-infrared emission line counts and luminosity functions from the HST WFC3 Infrared Spectroscopic Parallels (WISP) program for 29 fields observed using both the G102 and G141 grism. Using these derived emission line counts we make predictions for future space missions, like WFIRST, that will make extensive use of slitless grism spectroscopy in the near-IR over large areas of sky. The WISP survey is sensitive to fainter flux levels (3-5x10^-17 ergs/s/cm2) than the near-infrared grism missions aimed at baryonic acoustic oscillation cosmology (1-4x10^-16 ergs/s/cm2), allowing us to both investigate the fainter emission lines the large area surveys will be missing and make count predictions for the deeper grism pointings that are likely to be done over smaller areas. Cumulative number counts of 0.7<z<1.5 galaxies reach 10,000 square degrees above an H-alpha flux of 2x10^{-16} ergs/s/cm2. Galaxies with low H-alpha/[OIII] ratios are very rare at the brighter fluxes that future near-infrared grism surveys will probe; our survey finds no galaxies with H-alpha/[OIII < 0.95 that have H-alpha flux greater than 3x10^-16 ergs/s/cm2. We find good agreement between our derived luminosity functions and those from narrow band H-alpha surveys, like those of HiZELS (Sobral et al. 2013) and New Halpha (Ly et. 2011). The evolution in both the H-alpha luminosity function from z=0.3-1.5 and the [OIII] luminosity function from z=0.7-2.3 is almost entirely in the L* parameter, which steadily increases with redshift over those ranges. We will also present simulations of future large area near-infrared grism spectroscopy, based on the observed distributions of emission line fluxes, galaxy sizes, redshifts, H-alpha/[OIII] ratios, and equivalent widths seen in the WISP survey.
    01/2014;
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    ABSTRACT: Measurements of the chemical evolution of damped Ly-alpha systems (DLAs) show a linear decrease in the metallicity of DLAs with increasing redshift out to 4.7. We present evidence for a sudden decrease or break in the chemical abundances of damped Ly-alpha systems (DLAs) at 5, doubling the previous sample size at this redshift. This break may represent a transition in the nature of DLAs above 4.7. Specifically, the lower UV radiation field and higher density at high redshift increases the neutral fraction of gas inside halos, such as the lower metallicity cold streams, thereby contributing more significantly to the DLA population. This would result in more low metallicity systems being classified as DLAs. Even with the observed break, we show that the metallicity 'floor' of ~1/600 solar continues out to 5, despite our sensitivity for finding DLAs with much lower metallicities. In addition, we find preliminary evidence suggesting that the the comoving HI mass density and the incidence of DLAs at 5 may be decreasing or flattening out, even though they are predicted to increase, due to an increase in the neutrality of cold accreting gas as we approach the epoch of reionization.
    01/2014;
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    ABSTRACT: Ultra-faint star-forming galaxies produce a significant fraction of global star formation rate density at high redshifts. The magnification provided by strong gravitational lensing from massive clusters enables us to detect the faint background galaxies that are beyond our current detection limits. Using the massive lensing cluster Abell 1689 along with deep HST/WFC3 ultraviolet imaging (30 orbits in the F275W filter), we find that the UV luminosity function is steep down to very faint magnitudes (MUV = -13 AB mag) and shows no turnover. Our new HST program images Abell 1689 for 10 and 14 orbits in F225W and F336W bands, respectively. We again use the Lyman break technique to select star-forming galaxies as F225W and F336W “dropouts” at z=1.5 and z=2.7, respectively. Finally, we end up with a large sample of ultra-faint star-forming galaxies at the peak epoch of star formation, 1 < z < 3. We study the evolution of the faint-end slope of the UV luminosity function as well as a variety of properties of faint star-forming galaxies in this sample. We also measure the Lyman continuum escape fraction in these feeble sources, as they play an important role in making up the ionizing background radiation at both intermediate redshifts (1<z<3) and the epoch of reionization (z>6).
    01/2014;
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    ABSTRACT: We present a 48 orbit cycle-21 program to image three of the four Hubble Frontier Fields at near-ultraviolet wavelengths. Each lensing cluster will be observed for eight orbits in both the F275W and F336W filters. The primary science goals are to measure the luminosity functions of faint star-forming galaxies at 1.5<z<3, measure the Lyman continuum escape fractions, and study the sizes of star forming regions in galaxies at 1. Observations will likely begin in October. We will present the first images and compare to the existing optical Hubble images. In addition, we will show previous results from a deep near-UV imaging program in Abell 1689 as a demonstration of what can be done with these observations.
    01/2014;
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    ABSTRACT: Optical counterpart identification is a critical link in maximizing the science returns of the Herschel very wide-field survey data. Currently, the Sloan Digital Sky Survey (SDSS) is the best resource for optical counterpart identifications over such wide areas. However a large number of very bright FIR sources are not detected in the SDSS, and their true nature remains to be determined. Using the public HerMES data, we studied seven such sources that are within the CANDELS fields. To deal with the source blending problem, we used the near-IR or the optical images directly for position priors and decomposed these FIR sources. This new appraoch is an improvement over the previous decomposition efforts where the position priors are derived from the mid-IR data that still suffer from the source blending problem in the first place, and can be applied to the regions where the mid-IR data are not available. We found that in most cases the single Herschel sources are made of multiple components that may or may not be at the same redshifts. We showed that the major FIR contributors are all ULIRGs at z ~ 1 to 2, however most of them would not be selected as sub-mm galaxies (SMGs). Their host galaxies all have complicated morphologies indicative of merger or violent instability. Most of them do not seem to have significant AGN contribution, and their high L_IR imply dust-obscured star formation rates of a few hundred M_sun/yr. The existing stellar populations in the unobscured regions are heterogeneous, and show a wide range in stellar masses, ages and star formation histories. We propose a new diagnostics of high-redshift ULIRGs, which can be used to investigate the effectiveness of the current ULIRG phase in stellar mass assembly.
    The Astrophysical Journal Supplement Series 12/2013; 213(1). · 16.24 Impact Factor
  • 11/2013;
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    ABSTRACT: Of several dozen galaxies observed spectroscopically that are candidates for having a redshift (z) in excess of seven, only five have had their redshifts confirmed via Lyman α emission, at z = 7.008, 7.045, 7.109, 7.213 and 7.215 (refs 1-4). The small fraction of confirmed galaxies may indicate that the neutral fraction in the intergalactic medium rises quickly at z > 6.5, given that Lyman α is resonantly scattered by neutral gas. The small samples and limited depth of previous observations, however, makes these conclusions tentative. Here we report a deep near-infrared spectroscopic survey of 43 photometrically-selected galaxies with z > 6.5. We detect a near-infrared emission line from only a single galaxy, confirming that some process is making Lyman α difficult to detect. The detected emission line at a wavelength of 1.0343 micrometres is likely to be Lyman α emission, placing this galaxy at a redshift z = 7.51, an epoch 700 million years after the Big Bang. This galaxy's colours are consistent with significant metal content, implying that galaxies become enriched rapidly. We calculate a surprisingly high star-formation rate of about 330 solar masses per year, which is more than a factor of 100 greater than that seen in the Milky Way. Such a galaxy is unexpected in a survey of our size, suggesting that the early Universe may harbour a larger number of intense sites of star formation than expected.
    Nature 10/2013; 502(7472):524-7. · 38.60 Impact Factor
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    ABSTRACT: Out of several dozen z > 7 candidate galaxies observed spectroscopically, only five have been confirmed via Lyman-alpha emission, at z=7.008, 7.045, 7.109, 7.213 and 7.215. The small fraction of confirmed galaxies may indicate that the neutral fraction in the intergalactic medium (IGM) rises quickly at z > 6.5, as Lyman-alpha is resonantly scattered by neutral gas. However, the small samples and limited depth of previous observations makes these conclusions tentative. Here we report the results of a deep near-infrared spectroscopic survey of 43 z > 6.5 galaxies. We detect only a single galaxy, confirming that some process is making Lyman-alpha difficult to detect. The detected emission line at 1.0343 um is likely to be Lyman-alpha emission, placing this galaxy at a redshift z = 7.51, an epoch 700 million years after the Big Bang. This galaxy's colors are consistent with significant metal content, implying that galaxies become enriched rapidly. We measure a surprisingly high star formation rate of 330 Msol/yr, more than a factor of 100 greater than seen in the Milky Way. Such a galaxy is unexpected in a survey of our size, suggesting that the early universe may harbor more intense sites of star-formation than expected.
    10/2013;

Publication Stats

70 Citations
143.39 Total Impact Points

Institutions

  • 2014
    • University of California, Santa Barbara
      • Department of Physics
      Santa Barbara, California, United States
    • California Institute of Technology
      • Spitzer Science Center
      Pasadena, California, United States
  • 2013
    • University of Texas at Austin
      • Department of Astronomy
      Austin, Texas, United States
  • 2009–2010
    • University of California, San Diego
      • Center for Astrophysics and Space Sciences (CASS)
      San Diego, California, United States