ZFOURGE: Extreme 5007A˚\AA emission may be a common early-lifetime phase for star-forming galaxies at z>2.5z > 2.5

Using the \prospector\ spectral energy distribution (SED) fitting code, we analyze the properties of 19 Extreme Emission Line Galaxies (EELGs) identified in the bluest composite SED in the \zfourge\ survey at $2.5 \leq z \leq 4$. \prospector\ includes a physical model for nebular emission and returns probability distributions for stellar mass, stellar metallicity, dust attenuation, and nonparametric star formation history (SFH). The EELGs show evidence for a starburst in the most recent 50 Myr, with the median EELG having a specific star formation rate (sSFR) of 4.6 Gyr$^{-1}$ and forming 15\% of its mass in this short time. For a sample of more typical star-forming galaxies (SFGs) at the same redshifts, the median SFG has a sSFR of 1.1 Gyr$^{-1}$ and forms only $4\%$ of its mass in the last 50 Myr. We find that virtually all of our EELGs have rising SFHs, while most of our SFGs do not. From our analysis, we hypothesize that many, if not most, star-forming galaxies at $z \geq 2.5$ undergo an extreme H$\beta$+[\hbox{{\rm O}\kern 0.1em{\sc iii}}] emission line phase early in their lifetimes. In a companion paper, we obtain spectroscopic confirmation of the EELGs as part of our {\sc MOSEL} survey. In the future, explorations of uncertainties in modeling the UV slope for galaxies at $z>2$ are needed to better constrain their properties, e.g. stellar metallicities.Comment: 11 pages, 5 figures (main figure is fig 5), accepted for publication in Ap

R-process enrichment from a single event in an ancient dwarf galaxy

Elements heavier than zinc are synthesized through the (r)apid and (s)low neutron-capture processes. The main site of production of the r-process elements (such as europium) has been debated for nearly 60 years. Initial studies of chemical abundance trends in old Milky Way halo stars suggested continual r-process production, in sites like core-collapse supernovae. But evidence from the local Universe favors r-process production mainly during rare events, such as neutron star mergers. The appearance of a europium abundance plateau in some dwarf spheroidal galaxies has been suggested as evidence for rare r-process enrichment in the early Universe, but only under the assumption of no gas accretion into the dwarf galaxies. Cosmologically motivated gas accretion favors continual r-process enrichment in these systems. Furthermore, the universal r-process pattern has not been cleanly identified in dwarf spheroidals. The smaller, chemically simpler, and more ancient ultra-faint dwarf galaxies assembled shortly after the first stars formed, and are ideal systems with which to study nucleosynthesis events such as the r-process. Reticulum II is one such galaxy. The abundances of non-neutron-capture elements in this galaxy (and others like it) are similar to those of other old stars. Here, we report that seven of nine stars in Reticulum II observed with high-resolution spectroscopy show strong enhancements in heavy neutron-capture elements, with abundances that follow the universal r-process pattern above barium. The enhancement in this "r-process galaxy" is 2-3 orders of magnitude higher than that detected in any other ultra-faint dwarf galaxy. This implies that a single rare event produced the r-process material in Reticulum II. The r-process yield and event rate are incompatible with ordinary core-collapse supernovae, but consistent with other possible sites, such as neutron star mergers.Comment: Published in Nature, 21 Mar 2016: http://dx.doi.org/10.1038/nature1742

Observation of contemporaneous optical radiation from a gamma-ray burst

The origin of gamma-ray bursts (GRBs) has been enigmatic since their discovery. The situation improved dramatically in 1997, when the rapid availability of precise coordinates for the bursts allowed the detection of faint optical and radio afterglows - optical spectra thus obtained have demonstrated conclusively that the bursts occur at cosmological distances. But, despite efforts by several groups, optical detection has not hitherto been achieved during the brief duration of a burst. Here we report the detection of bright optical emission from GRB990123 while the burst was still in progress. Our observations begin 22 seconds after the onset of the burst and show an increase in brightness by a factor of 14 during the first 25 seconds; the brightness then declines by a factor of 100, at which point (700 seconds after the burst onset) it falls below our detection threshold. The redshift of this burst, approximately 1.6, implies a peak optical luminosity of 5 times 10^{49} erg per second. Optical emission from gamma-ray bursts has been generally thought to take place at the shock fronts generated by interaction of the primary energy source with the surrounding medium, where the gamma-rays might also be produced. The lack of a significant change in the gamma-ray light curve when the optical emission develops suggests that the gamma-rays are not produced at the shock front, but closer to the site of the original explosion.Comment: 10 pages, 2 figures. Accepted for publication in Nature. For additional information see http://www.umich.edu/~rotse

A magnified young galaxy from about 500 million years after the Big Bang

Re-ionization of the intergalactic medium occurred in the early Universe at redshift z ≈ 6-11, following the formation of the first generation of stars. Those young galaxies (where the bulk of stars formed) at a cosmic age of less than about 500 million years (z ≲ 10) remain largely unexplored because they are at or beyond the sensitivity limits of existing large telescopes. Understanding the properties of these galaxies is critical to identifying the source of the radiation that re-ionized the intergalactic medium. Gravitational lensing by galaxy clusters allows the detection of high-redshift galaxies fainter than what otherwise could be found in the deepest images of the sky. Here we report multiband observations of the cluster MACS J1149+2223 that have revealed (with high probability) a gravitationally magnified galaxy from the early Universe, at a redshift of z = 9.6 ± 0.2 (that is, a cosmic age of 490 ± 15 million years, or 3.6 per cent of the age of the Universe). We estimate that it formed less than 200 million years after the Big Bang (at the 95 per cent confidence level), implying a formation redshift of ≲14. Given the small sky area that our observations cover, faint galaxies seem to be abundant at such a young cosmic age, suggesting that they may be the dominant source for the early re-ionization of the intergalactic medium

On the Origin of S0 Galaxies

I will review the basic properties of S0 galaxies in the local Universe in relation to both elliptical and spiral galaxies, their neighbours on the Hubble sequence, and also in relation to dwarf spheroidal (dSph) galaxies. This will include colours, luminosities, spectral features, information about the age and metallicity composition of their stellar populations and globular clusters, about their ISM content, as well as kinematic signatures and their implications for central black hole masses and past interaction events, and the number ratios of S0s to other galaxy types in relation to environmental galaxy density. I will point out some caveats as to their morphological discrimination against other classes of galaxies, discuss the role of dust and the wavelength dependence of bulge/disk light ratios. These effects are of importance for investigations into the redshift evolution of S0 galaxies -- both as individual objects and as a population. The various formation and transformation scenarios for S0 and dSph galaxies will be presented and confronted with the available observations.Comment: Invited Review, 18 pages, ``BARS 2004'' Conference, South Africa, June 2004, eds.: K. C. Freeman, D. L. Block, I. Puerari, R. Groess, Kluwer, in pres

The expansion field: The value of H_0

Any calibration of the present value of the Hubble constant requires recession velocities and distances of galaxies. While the conversion of observed velocities into true recession velocities has only a small effect on the result, the derivation of unbiased distances which rest on a solid zero point and cover a useful range of about 4-30 Mpc is crucial. A list of 279 such galaxy distances within v<2000 km/s is given which are derived from the tip of the red-giant branch (TRGB), from Cepheids, and from supernovae of type Ia (SNe Ia). Their random errors are not more than 0.15 mag as shown by intercomparison. They trace a linear expansion field within narrow margins from v=250 to at least 2000 km/s. Additional 62 distant SNe Ia confirm the linearity to at least 20,000 km/s. The dispersion about the Hubble line is dominated by random peculiar velocities, amounting locally to <100 km/s but increasing outwards. Due to the linearity of the expansion field the Hubble constant H_0 can be found at any distance >4.5 Mpc. RR Lyr star-calibrated TRGB distances of 78 galaxies above this limit give H_0=63.0+/-1.6 at an effective distance of 6 Mpc. They compensate the effect of peculiar motions by their large number. Support for this result comes from 28 independently calibrated Cepheids that give H_0=63.4+/-1.7 at 15 Mpc. This agrees also with the large-scale value of H_0=61.2+/-0.5 from the distant, Cepheid-calibrated SNe Ia. A mean value of H_0=62.3+/-1.3 is adopted. Because the value depends on two independent zero points of the distance scale its systematic error is estimated to be 6%. Typical errors of H_0 come from the use of a universal, yet unjustified P-L relation of Cepheids, the neglect of selection bias in magnitude-limited samples, or they are inherent to the adopted models.Comment: 44 pages, 4 figures, 6 tables, accepted for publication in the Astronony and Astrophysics Review 15

The evolution of early-type galaxies in distant clusters. I. Surface photometry and structural parameters for 53 galaxies in the z=0.33 cluster Cl 1358+62

Using wide-field, two-color Hubble Space Telescope (HST) imaging of the cluster Cl 1358 + 62 (z = 0.33), we derive structural parameters for a large, magnitude-limited sample of cluster members. These structural parameters are combined with accurate velocity dispersions in another paper to investigate the fundamental plane in the cluster. We fit integrated r(1/4) laws to the integrated surface brightness profiles and fit two-dimensional r(1/4)-law model galaxies to the images directly. A comparison of the results from the two methods shows that the derived half-light radii, r(e), agree very well, with an rms scatter of only 13%. The half-light radii range from approximately 1 to 20 kpc with a median of about 3 kpc (H(0) = 65 km s(-1) Mpc(-1), q(0) = 0.1). We investigated the stability of r(e) by comparing the r(1/4)-law fits to the half-light radii derived using other commonly used surface brightness profiles. In particular, we fit Sersic r(1/n) laws (finding the best-fit ii in the range n = 1-6) and superpositions of r(1/4)-law bulges with exponential disks. The half-light radii derived from the best-fit Sersic profiles varied with respect to r(e) from the r(1/4)-law fits by only 1% in the median, but with a standard deviation of more than 40% in r(e). For the bulge + disk fits, the derived half-light radii were offset from r(e) of the r(1/4)-law fits by 10% in the mean, also showing a large standard deviation of more than 40%. By comparing the fitted half-light radii from the Sersic laws with those derived from the bulge + disk fitting, one also finds a large scatter of 30%. Based on these tests, we conclude that, in general, half-light radii are only measured with a typical accuracy of 30%-40%. While there are large uncertainties in half-light radii, these do not impact the subsequent fundamental plane analysis because the combination r(I)(0.76), which enters the fundamental plane, is extremely stable. The rms scatter in r(1)0.76 is less than 3%, regardless of the form of the profile fit to the galaxies. By fitting bulge + disk profiles, we find that the median bulge fraction of the sample is 84% and that the few E + A galaxies in this sample have disks which make up about 10%-35% of their total light. These results are consistent with the residuals from fitting two-dimensional r(1/4)-law models directly to the galaxies, in which disklike structures are revealed in about half of the sample. Two of the three E + A galaxies show spiral arm structure

The evolution of early-type galaxies in distant clusters. II. Internal kinematics of 55 galaxies in the z=0.33 cluster Cl 1358+62

We define a large sample of galaxies for use in a study of the fundamental plane in the intermediate redshift cluster Cl 1358 + 62 at z = 0.33. We have analyzed high-resolution spectra for 55 members of the cluster. The data were acquired with the Low-Resolution Imaging Spectrograph on the Keck 1 10 m telescope. A new algorithm for measuring velocity dispersions is presented and used to measure the internal kinematics of the galaxies. This algorithm has been tested against the Fourier fitting method so that the data presented here can be compared with those measured previously in nearby galaxies. We have measured central velocity dispersions suitable for use in a fundamental plane analysis. The data have a high signal-to-noise ratio (S/N) and the resulting random errors on the dispersions are very low, typically less that 5%. Uncertainties due to mismatch of the stellar templates have been minimized through several tests, and the total systematic error is of order similar to 5%. Good seeing enabled us to measure velocity dispersion profiles and rotation curves for most of the sample, and although a large fraction of the galaxies display a high level of rotation, the gradients of the total second moment of the kinematics are all very regular and similar to those in nearby galaxies. We conclude that the data therefore can be reliably corrected for aperture size in a manner consistent with nearby galaxy samples.</p

The evolution of early-type galaxies in distant clusters. I. Surface photometry and structural parameters for 53 galaxies in the z=0.33 cluster Cl 1358+62

Using wide-field, two-color Hubble Space Telescope (HST) imaging of the cluster Cl 1358 + 62 (z = 0.33), we derive structural parameters for a large, magnitude-limited sample of cluster members. These structural parameters are combined with accurate velocity dispersions in another paper to investigate the fundamental plane in the cluster. We fit integrated r(1/4) laws to the integrated surface brightness profiles and fit two-dimensional r(1/4)-law model galaxies to the images directly. A comparison of the results from the two methods shows that the derived half-light radii, r(e), agree very well, with an rms scatter of only 13%. The half-light radii range from approximately 1 to 20 kpc with a median of about 3 kpc (H(0) = 65 km s(-1) Mpc(-1), q(0) = 0.1).We investigated the stability of r(e) by comparing the r(1/4)-law fits to the half-light radii derived using other commonly used surface brightness profiles. In particular, we fit Sersic r(1/n) laws (finding the best-fit ii in the range n = 1-6) and superpositions of r(1/4)-law bulges with exponential disks. The half-light radii derived from the best-fit Sersic profiles varied with respect to r(e) from the r(1/4)-law fits by only 1% in the median, but with a standard deviation of more than 40% in r(e). For the bulge + disk fits, the derived half-light radii were offset from r(e) of the r(1/4)-law fits by 10% in the mean, also showing a large standard deviation of more than 40%. By comparing the fitted half-light radii from the Sersic laws with those derived from the bulge + disk fitting, one also finds a large scatter of 30%. Based on these tests, we conclude that, in general, half-light radii are only measured with a typical accuracy of 30%-40%.While there are large uncertainties in half-light radii, these do not impact the subsequent fundamental plane analysis because the combination r(I)(0.76), which enters the fundamental plane, is extremely stable. The rms scatter in r(1)0.76 is less than 3%, regardless of the form of the profile fit to the galaxies.By fitting bulge + disk profiles, we find that the median bulge fraction of the sample is 84% and that the few E + A galaxies in this sample have disks which make up about 10%-35% of their total light. These results are consistent with the residuals from fitting two-dimensional r(1/4)-law models directly to the galaxies, in which disklike structures are revealed in about half of the sample. Two of the three E + A galaxies show spiral arm structure.</p