We derive new self-consistent theoretical UV, optical, and IR diagnostics for the interstellar medium (ISM) pressure and electron density in the ionized nebulae of star-forming galaxies. Our UV ...diagnostics utilize the intercombination, forbidden, and resonance lines of silicon, carbon, aluminum, neon, and nitrogen. We also calibrate the optical and IR forbidden lines of oxygen, argon, nitrogen, and sulfur. We show that line ratios used as ISM pressure diagnostics depend on the gas-phase metallicity with a residual dependence on the ionization parameter of the gas. In addition, the traditional electron density diagnostic S ii λ6731/S ii λ6717 is strongly dependent on the gas-phase metallicity. We show how different emission-line ratios are produced in different ionization zones in our theoretical nebulae. The S ii and O ii ratios are produced in different zones and should not be used interchangeably to measure the electron density of the gas unless the electron temperature is known to be constant. We review the temperature and density distributions observed within H ii regions and discuss the implications of these distributions on measuring the electron density of the gas. Many H ii regions contain radial variations in density. We suggest that the ISM pressure is a more meaningful quantity to measure in H ii regions or galaxies. Specific combinations of line ratios can cover the full range of ISM pressures (4 < log(P/k) < 9). As H ii regions become resolved at increasingly high redshift through the next generation of telescopes, we anticipate that these diagnostics will be important for understanding the conditions around the young, hot stars from the early universe to the present day.
We measure the photometric properties of 105 giant arcs that were identified in systematic searches for galaxy-cluster-scale strong lenses in the Second Red-Sequence Cluster Survey and the Sloan ...Digital Sky Survey. The cluster lenses span 0.2 < z sub(l) < 1.2 in redshift, with a median z sub(l) = 0.58. Using broadband color criteria we sort the entire arc sample into redshift bins based on u-g and g-r colors, and also r-z colors for the ~90% of arcs that have z-band data. This analysis yields broad redshift constraints with 71 sub(-4) super(+5)% of the arcs at z > or = 1.0, 64 sub(-4) super(+6)% at z > 1.4, 56 sub(-4) super(+5)% at z > or = 1.9, and 21 sub(-2) super(+4)% at z > or = 2.7. The remaining 29 sub(-5) super(+03)% have z < 1. The inferred median redshift is z sub(s) = 2.0 + or - 0.1, in good agreement with a previous determination from a smaller sample of brighter arcs (g <, approximate 22.5). This agreement confirms that z sub(s) = 2.0 + or - 0.1 is the typical redshift for giant arcs with g <, approximate 24 that are produced by cluster-scale strong lenses and that there is no evidence for strong evolution in the redshift distribution of arcs over a wide range of g-band magnitudes (20 < or = g < or = 24). Establishing that half of all giant arcs are at z >, approximate 2 contributes significantly toward relieving the tension between the number of arcs observed and the number expected in a ACDM cosmology, but there is considerable evidence to suggest that a discrepancy persists. Additionally, this work confirms that forthcoming large samples of giant arcs will supply the observational community with many magnified galaxies at z >, approximate 2.
We present strong-lensing models as well as mass and magnification maps for the cores of the six Hubble Space Telescope (HST) Frontier Fields galaxy clusters. Our parametric lens models are ...constrained by the locations and redshifts of multiple image systems of lensed background galaxies. We use a combination of photometric redshifts and spectroscopic redshifts of the lensed background sources obtained by us (for A2744 and AS1063), collected from the literature, or kindly provided by the lensing community. Using our results, we (1) compare the derived mass distribution of each cluster to its light distribution, (2) quantify the cumulative magnification power of the HST Frontier Fields clusters, (3) describe how our models can be used to estimate the magnification and image multiplicity of lensed background sources at all redshifts and at any position within the cluster cores, and (4) discuss systematic effects and caveats resulting from our modeling methods. We specifically investigate the effect of the use of spectroscopic and photometric redshift constraints on the uncertainties of the resulting models. We find that the photometric redshift estimates of lensed galaxies are generally in excellent agreement with spectroscopic redshifts, where available. However, the flexibility associated with relaxed redshift priors may cause the complexity of large-scale structure that is needed to account for the lensing signal to be underestimated. Our findings thus underline the importance of spectroscopic arc redshifts, or tight photometric redshift constraints, for high precision lens models. All products from our best-fit lens models (magnification, convergence, shear, deflection field) and model simulations for estimating errors are made available via the Mikulski Archive for Space Telescopes.
Abstract We present measurements of the surface density of star formation, the star-forming clump luminosity function, and the clump size distribution function, for the lensed galaxy ...SGAS J111020.0+645950.8 at a redshift of z = 2.481. The physical size scales that we probe, radii r = 30–50 pc, are considerably smaller scales than have yet been studied at these redshifts. The star formation surface density we find within these small clumps is consistent with surface densities measured previously for other lensed galaxies at similar redshift. Twenty-two percent of the rest-frame ultraviolet light in this lensed galaxy arises from small clumps, with pc. Within the range of overlap, the clump luminosity function measured for this lensed galaxy is remarkably similar to those of galaxies. In this galaxy, star-forming regions smaller than 100 pc—physical scales not usually resolved at these redshifts by current telescopes—are important locations of star formation in the distant universe. If this galaxy is representative, this may contradict the theoretical picture in which the critical size scale for star formation in the distant universe is of the order of 1 kpc. Instead, our results suggest that current telescopes have not yet resolved the critical size scales of star-forming activity in galaxies over most of cosmic time.
We present optical and near-IR imaging and spectroscopy of SGAS J 105039.6+001730, a strongly lensed galaxy at z = 3.6252 magnified by >30x, and derive its physical properties. We measure a stellar ...mass of log(M sub(*)/M sub(middot in circle)) = 9.5 + or - 0.35, star formation rates from OII 2.2.3727 and H beta of 55 + or - 25 and 84 + or - 24 M sub(middot in circle) yr super(-1), respectively, an electron density of n sub(e) < or =, slant 10 super(3) cm super(-2), an electron temperature of T sub(e) < or =, slant 14,000 K, and a metallicity of 12 + log(O/H) = 8.3 + or - 0.1. The strong C III lambdalambda1907,1909 emission and abundance ratios of C, N, O, and Si are consistent with well-studied starbursts at z ~ 0 with similar metallicities. Strong P Cygni lines and He II lambda1640 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 suggested 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 probe the spatial distribution of outflowing gas along four lines of sight separated by up to 6 kpc in a gravitationally lensed star-forming galaxy at z = 1.70. Using Mg II and Fe II emission and ...absorption as tracers, we find that the clumps of star formation are driving galactic outflows with velocities of − 170 to − 250 km/s. The velocities of Mg II emission are redshifted with respect to the systemic velocities of the galaxy, consistent with being backscattered. By contrast, the Fe II fluorescent emission lines are either slightly blueshifted or at the systemic velocity of the galaxy. Taken together, the velocity structure of the Mg II and Fe II emission is consistent with arising through scattering in galactic winds. Assuming a thin shell geometry for the outflowing gas, the estimated masses carried out by these outflows are large (approx 30-50 M/yr), with mass loading factors several times the star formation rate. Almost 20 per cent to 50 per cent of the blueshifted absorption probably escapes the gravitational potential of the galaxy. In this galaxy, the outflow is 'locally sourced', that is, the properties of the outflow in each line of sight are dominated by the properties of the nearest clump of star formation; the wind is not global to the galaxy. The mass outflow rates and the momentum flux carried out by outflows in individual star-forming knots of this object are comparable to that of starburst galaxies in the local Universe.
Abstract We present the discovery of the most distant, dynamically relaxed cool core cluster, SPT-CL J2215−3537 (SPT2215), and its central brightest cluster galaxy (BCG) at z = 1.16. Using new X-ray ...observations, we demonstrate that SPT2215 harbors a strong cool core with a central cooling time of 200 Myr (at 10 kpc) and a maximal intracluster medium cooling rate of 1900 ± 400 M ⊙ yr −1 . This prodigious cooling may be responsible for fueling the extended, star-forming filaments observed in Hubble Space Telescope imaging. Based on new spectrophotometric data, we detect bright O ii emission in the BCG, implying an unobscured star formation rate (SFR) of 320 − 140 + 230 M ⊙ yr −1 . The detection of a weak radio source (2.0 ± 0.8 mJy at 0.8 GHz) suggests ongoing feedback from an active galactic nucleus (AGN), though the implied jet power is less than half the cooling luminosity of the hot gas, consistent with cooling overpowering heating. The extreme cooling and SFR of SPT2215 are rare among known cool core clusters, and it is even more remarkable that we observe these at such high redshift, when most clusters are still dynamically disturbed. The high mass of this cluster, coupled with the fact that it is dynamically relaxed with a highly isolated BCG, suggests that it is an exceptionally rare system that must have formed very rapidly in the early universe. Combined with the high SFR, SPT2215 may be a high- z analog of the Phoenix cluster, potentially providing insight into the limits of AGN feedback and star formation in the most massive galaxies.
We study the mass distribution of a sample of 28 galaxy clusters using strong and weak lensing observations. The clusters are selected via their strong lensing properties as part of the Sloan Giant ...Arcs Survey (SGAS) from the Sloan Digital Sky Survey (SDSS). Mass modelling of the strong lensing information from the giant arcs is combined with weak lensing measurements from deep Subaru/Suprime-cam images to primarily obtain robust constraints on the concentration parameter and the shape of the mass distribution. We find that the concentration c
vir is a steep function of the mass, c
vir∝M
−0.59±0.12
vir, with the value roughly consistent with the lensing-bias-corrected theoretical expectation for high-mass (∼1015 h
−1 M⊙) clusters. However, the observationally inferred concentration parameters appear to be much higher at lower masses (∼1014 h
−1 M⊙), possibly a consequence of the modification to the inner density profiles provided by baryon cooling. The steep mass-concentration relation is also supported from direct stacking analysis of the tangential shear profiles. In addition, we explore the 2D shape of the projected mass distribution by stacking weak lensing shear maps of individual clusters with prior information on the position angle from strong lens modelling, and find significant evidence for a large mean ellipticity with the best-fitting value of 〈e〉= 0.47 ± 0.06 for the mass distribution of the stacked sample. We find that the luminous cluster member galaxy distribution traces the overall mass distribution very well, although the distribution of fainter cluster galaxies appears to be more extended than the total mass.
Abstract Using the combined resolving power of the Hubble Space Telescope and gravitational lensing, we resolve star-forming structures in a galaxy on scales much smaller than the usual kiloparsec ...diffraction limit of HST . SGAS J111020.0+645950.8 is a clumpy, star-forming galaxy lensed by the galaxy cluster SDSS J1110+6459 at , with a total magnification across the entire arc. We use a hybrid parametric/non-parametric strong lensing mass model to compute the deflection and magnification of this giant arc, reconstruct the light distribution of the lensed galaxy in the source plane, and resolve the star formation into two dozen clumps. We develop a forward-modeling technique to model each clump in the source plane. We ray-trace the model to the image plane, convolve with the instrumental point-spread function (PSF), and compare with the GALFIT model of the clumps in the image plane, which decomposes clump structure from more extended emission. This technique has the advantage, over ray-tracing, of accounting for the asymmetric lensing shear of the galaxy in the image plane and the instrument PSF. At this resolution, we can begin to study star formation on a clump-by-clump basis, toward the goal of understanding feedback mechanisms and the buildup of exponential disks at high redshift.
PDF
