arXiv subjects

Arthur M. Wolfe

Publications and source records attributed to Arthur M. Wolfe.

At least 19 recordsLinked to original sources

arXiv2017

[CII] 158 micron Emission from the Host Galaxies of Damped Lyman Alpha Systems

Gas surrounding high redshift galaxies has been studied through observations of absorption line systems toward background quasars for decades. However, it has proven difficult to identify and characterize the galaxies associated with these absorbers due to the intrinsic faintness of the galaxies compared to the quasars at optical wavelengths. Utilizing the Atacama Large Millimeter/Submillimeter Array, we report on detections of [CII] 158 micron line and dust continuum emission from two galaxies associated with two such absorbers at a redshift of z~4. Our results indicate that the hosts of these high-metallicity absorbers have physical properties similar to massive star-forming galaxies and are embedded in enriched neutral hydrogen gas reservoirs that extend well beyond the star-forming interstellar medium of these galaxies.

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arXiv2016

C II radiative cooling of the Galactic diffuse interstellar medium: Insight about the star formation in Damped Lyman-alpha systems

The far-infrared [C II] 158 micrometer fine structure transition is considered to be a dominant coolant in the interstellar medium. For this reason, under the assumption of a thermal steady state, it may be used to infer the heating rate and, in turn, the star formation rate in local, as well as in high redshift systems. In this work, radio and ultraviolet observations of the Galactic interstellar medium are used to understand whether C II is indeed a good tracer of the star formation rate. For a sample of high Galactic latitude sightlines, direct measurements of the temperature indicate the presence of C II in both the cold and the warm phases of the diffuse interstellar gas. The cold gas fraction (~ 10 - 50% of the total neutral gas column density) is not negligible even at high Galactic latitude. It is shown that, to correctly estimate the star formation rate, C II cooling in both the phases should hence be considered. The simple assumption, that the [C II] line originates only from either the cold or the warm phase, significantly underpredicts or overpredicts the star formation rate, respectively. These results are particularly important in the context of the Damped Lyman-alpha systems for which a similar method is often used to estimate the star formation rate. The derived star formation rates in such cases may not be reliable if the temperature of the gas under consideration is not constrained independently.

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arXiv2014

The most metal-rich damped Lyman alpha systems at z>1.5 I: The Data

We present HIRES observations for 30 damped Lyman alpha systems, selected on the basis of their large metal column densities from previous, lower resolution data. The measured metal column densities for Fe, Zn, S, Si, Cr, Mn, and Ni are provided for these 30 systems. Combined with previously observed large metal column density damped Lyman alpha systems, we present a sample of 44 damped Lyman alpha systems observed with high resolution spectrographs (R~30000). These damped Lyman alpha systems probe the most chemically evolved systems at redshifts greater than 1.5. We discuss the context of our sample with the general damped Lyman alpha population, demonstrating that we are probing the top 10% of metal column densities with our sample. In a companion paper, we will present an analysis of the sample's elemental abundances in the context of galactic chemical enrichment.

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arXiv2014

Directly imaging damped Ly-alpha galaxies at z>2. II: Imaging and spectroscopic observations of 32 quasar fields

Damped Ly-alpha absorbers (DLAs) are a well-studied class of absorption line systems, and yet the properties of their host galaxies remain largely unknown. To investigate the origin of these systems, we have conducted an imaging survey of 32 quasar fields with intervening DLAs between z~1.9-3.8, leveraging a technique that allows us to image galaxies at any small angular separation from the background quasars. In this paper, we present the properties of the targeted DLA sample, new imaging observations of the quasar fields, and the analysis of new and archival spectra of the background quasars.

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arXiv2014

The Rapid Decline in Metallicity of Damped Ly-alpha Systems at z~5

We present evidence that the cosmological mean metallicity of neutral atomic hydrogen gas shows a sudden decrease at z>4.7 down to =-2.03(+0.09-0.11), which is 6 sigma 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 8 new damped Ly-alpha (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 ultra-violet 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, 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.

astro-ph.CO↗

arXiv2013

Spatially Resolved Emission of a High Redshift DLA Galaxy with the Keck/OSIRIS IFU

We present the first Keck/OSIRIS infrared IFU observations of a high redshift damped Lyman-alpha (DLA) galaxy detected in the line of sight to a background quasar. By utilizing the Laser Guide Star Adaptive Optics (LGSAO) to reduce the quasar PSF to FWHM~0.15 arcsec, we were able to search for and map the foreground DLA emission free from the quasar contamination. We present maps of the H-alpha and [OIII] $λλ$ 5007, 4959 emission of DLA 2222-0946 at a redshift of z ~ 2.35. From the composite spectrum over the H-alpha emission region we measure a star formation rate of 9.5 $\pm$ 1.0 M$_{\odot}$ year$^{-1}$ and a dynamical mass, M$_{dyn}$ = 6.1 x 10$^9$ M$_{\odot}$. The average star formation rate surface density is < Σ_{SFR} > = 0.55 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$, with a central peak of 1.7 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$. Using the standard Kennicutt-Schmidt relation, this corresponds to a gas mass surface density of $Σ_{gas}$ = 243 M$_{\odot}$ pc$^{-2}$. Integrating over the size of the galaxy we find a total gas mass of M$_{gas}$ = 4.2 x 10$^9$ M$_{\odot}$. We estimate the gas fraction of DLA 2222-0946 to be $f_{gas}$ ~ 40%. We detect [NII]$λ$6583 emission at 2.5 sigma significance with a flux corresponding to a metallicity of 75% solar. Comparing this metallicity with that derived from the low-ion absorption gas ~6 kpc away, ~30% solar, indicates possible evidence for a metallicity gradient or enriched in/outflow of gas. Kinematically, both H-alpha and [OIII] emission show relatively constant velocity fields over the central galactic region. While we detect some red and blueshifted clumps of emission, they do not correspond with rotational signatures that support an edge-on disk interpretation.

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arXiv2013

UVUDF: Ultraviolet Imaging of the Hubble Ultradeep Field with Wide-field Camera 3

We present an overview of a 90-orbit Hubble Space Telescope treasury program to obtain near ultraviolet imaging of the Hubble Ultra Deep Field using the Wide Field Camera 3 UVIS detector with the F225W, F275W, and F336W filters. This survey is designed to: (i) Investigate the episode of peak star formation activity in galaxies at 1<z<2.5; (ii) Probe the evolution of massive galaxies by resolving sub-galactic units (clumps); (iii) Examine the escape fraction of ionizing radiation from galaxies at z~2-3; (iv) Greatly improve the reliability of photometric redshift estimates; and (v) Measure the star formation rate efficiency of neutral atomic-dominated hydrogen gas at z~1-3. In this overview paper, we describe the survey details and data reduction challenges, including both the necessity of specialized calibrations and the effects of charge transfer inefficiency. We provide a stark demonstration of the effects of charge transfer inefficiency on resultant data products, which when uncorrected, result in uncertain photometry, elongation of morphology in the readout direction, and loss of faint sources far from the readout. We agree with the STScI recommendation that future UVIS observations that require very sensitive measurements use the instrument's capability to add background light through a "post-flash". Preliminary results on number counts of UV-selected galaxies and morphology of galaxies at z~1 are presented. We find that the number density of UV dropouts at redshifts 1.7, 2.1, and 2.7 is largely consistent with the number predicted by published luminosity functions. We also confirm that the image mosaics have sufficient sensitivity and resolution to support the analysis of the evolution of star-forming clumps, reaching 28-29th magnitude depth at 5 sigma in a 0.2 arcsecond radius aperture depending on filter and observing epoch.

astro-ph.CO↗

arXiv2013

The Fundamental Plane of Damped Lyman Alpha Systems

Using a sample of 100 H I - selected damped Lyman alpha (DLA) systems, observed with the High Resolution Echelle Spectrometer on the Keck I telescope, we present evidence that the scatter in the well-studied correlation between the redshift and metallicity of a DLA is largely due to the existence of a mass-metallicity relationship at each redshift. To describe the fundamental relations that exist between redshift, metallicity and mass, we use a fundamental plane description, which is described by the following equation: [M/H]=(-1.9+-0.5)+(0.74+-0.21)logdv_90-(0.32+-0.06)z. Here, we assert that the velocity width, dv_90, which is defined as the velocity interval containing 90% of the integrated optical depth, traces the mass of the underlying dark matter halo. This description provides two significant improvements over the individual descriptions of the mass-metallicity correlation and metallicity-redshift correlation. Firstly, the fundamental equation reduces the scatter around both relationships by about 20%, providing a more stringent constraint on numerical simulations modeling DLAs. Secondly, it confirms that the dark matter halos that host DLAs satisfy a mass-metallicity relationship at each redshift between redshifts 2 through 5.

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arXiv2012

Metallicity Evolution of Damped Lyman-alpha Systems out to z~5

We present chemical abundance measurements for 47 damped Lyman-alpha systems (DLAs), 30 at z>4, observed with the Echellette Spectrograph and Imager and the High Resolution Echelle Spectrometer on the Keck telescopes. HI column densities of the DLAs are measured with Voigt profile fits to the Lyman-alpha profiles, and we find an increased number of false DLA identifications with SDSS at z>4 due to the increased density of the Lyman-alpha forest. Ionic column densities are determined using the apparent optical depth method, and we combine our new metallicity measurements with 195 from previous surveys to determine the evolution of the cosmic metallicity of neutral gas. We find the metallicity of DLAs decreases with increasing redshift, improving the significance of the trend and extending it to higher redshifts, with a linear fit of -0.22+-0.03 dex per unit redshift from z=0.09-5.06. The metallicity 'floor' of ~1/600 solar continues out to z~5, despite our sensitivity for finding DLAs with much lower metallicities. However, this floor is not statistically different from a steep tail to the distribution. We also find that the intrinsic scatter of metallicity among DLAs of ~0.5 dex continues out to z~5. In addition, the metallicity distribution and the alpha/Fe ratios of z>2 DLAs are consistent with being drawn from the same parent population with those of halo stars. It is therefore possible that the halo stars in the Milky Way formed out of gas that commonly exhibits DLA absorption at z>2.

astro-ph.CO↗

arXiv2011

Star Formation from DLA Gas in the Outskirts of Lyman Break Galaxies at z~3

We present evidence for spatially extended low surface brightness emission around Lyman break galaxies (LBGs) in the V band image of the Hubble Ultra Deep Field, corresponding to the z~3 rest-frame FUV light, which is a sensitive measure of star formation rates (SFRs). We find that the covering fraction of molecular gas at z~3 is not adequate to explain the emission in the outskirts of LBGs, while the covering fraction of neutral atomic-dominated hydrogen gas at high redshift is sufficient. We develop a theoretical framework to connect this emission around LBGs to the expected emission from neutral H I gas i.e., damped Lyman alpha systems (DLAs), using the Kennicutt-Schmidt (KS) relation. Working under the hypothesis that the observed FUV emission in the outskirts of LBGs is from in situ star formation in atomic-dominated hydrogen gas, the results suggest that the SFR efficiency in such gas at z~3 is between factors of 10 and 50 lower than predictions based on the local KS relation. The total SFR density in atomic-dominated gas at z~3 is constrained to be ~10% of that observed from the inner regions of LBGs. In addition, the metals produced by in situ star formation in the outskirts of LBGs yield metallicities comparable to those of DLAs, which is a possible solution to the "Missing Metals" problem for DLAs. Finally, the atomic-dominated gas in the outskirts of galaxies at both high and low redshifts has similar reduced SFR efficiencies and is consistent with the same power law.

astro-ph.CO↗

arXiv2011

Spectral Polarization of the Redshifted 21 cm Absorption Line Toward 3C 286

A re-analysis of the Stokes-parameter spectra obtained of the z=0.692 21 cm absorption line toward 3C 286 shows that our original claimed detection of Zeeman splitting by a line-of-sight magnetic field, B_los = 87 microgauss is incorrect. Because of an insidious software error, what we reported as Stokes V is actually Stokes U: the revised Stokes V spectrum indicates a 3-sigma upper limit of B_los < 17 microgauss. The correct analysis reveals an absorption feature in fractional polarization that is offset in velocity from the Stokes I spectrum by -1.9 km/s. The polarization position-angle spectrum shows a dip that is also significantly offset from the Stokes I feature, but at a velocity that differs slightly from the absorption feature in fractional polarization. We model the absorption feature with 3 velocity components against the core-jet structure of 3C 286. Our chisquare minimization fitting results in components with differing (1) ratios of H I column density to spin temperature, (2) velocity centroids, and (3) velocity dispersions. The change in polarization position angle with frequency implies incomplete coverage of the background jet source by the absorber. It also implies a spatial variation of the polarization position angle across the jet source, which is observed at frequencies higher than the 839.4 MHz absorption frequency. The multi-component structure of the gas is best understood in terms of components with spatial scales of ~100 pc comprised of hundreds of low-temperature (T < 200 K) clouds with linear dimensions of about 1 pc.

astro-ph.CO↗

arXiv2010

On the Analysis of DLA Kinematics

We discuss two mistreatments of damped Lya (DLA) kinematic analysis that were first performed by Haehnelt, Steinmetz, & Rauch (1998; hereafter HSR98) and have recently been repeated by Hong et al. (2010; arXiv:1008.4242v1, arXiv:1008.4242v2; hereafter H10). Each mistreatment led to the improper excising of simulated absorption profiles. Specifically, their analyses are strictly biased against DLA sightlines that have low HI column density log NHI < 20.5, very high NHI values, and (for all NHI) sightlines with low velocity width Dv (<30 km/s for HSR98; <[20-30] km/s for H10). None of these biases exist in the observational analysis. We suspect these mistreatments compromise the results that followed. Hopefully this posting will prevent their repetition in the future.

astro-ph.CO↗

arXiv2010

Understanding Physical Conditions in High Redshift Galaxies through C I Fine Structure Lines: Data and Methodology

We probe the physical conditions in high redshift galaxies, specifically, the Damped Lyman-alpha Systems (DLAs) using neutral carbon (CI) fine structure lines and molecular hydrogen (H2). We report five new detections of CI and analyze the CI in an additional 2 DLAs with previously published data. We also present one new detection of H2 in a DLA. We present a new method of analysis that simultaneously constrains \emph{both} the volume density and the temperature of the gas, as opposed to previous studies that a priori assumed a gas temperature. We use only the column density of CI measured in the fine structure states and the assumption of ionization equilibrium in order to constrain the physical conditions in the gas. We present a sample of 11 CI velocity components in 6 DLAs and compare their properties to those derived by the global CII* technique. The resulting median values for this sample are: = 69 cm^{-3}, = 50 K, and = 3.86 cm^{-3} K, with standard deviations, sigma_{n(HI)} = 134 cm^{-3}, sigma_T = 52 K, and sigma_{log(P/k)} = 3.68 cm^{-3} K. This can be compared with the integrated median values for the same DLAs : = 2.8 cm^{-3}, = 139 K, and = 2.57 cm^{-3} K, with standard deviations sigma_{n(HI)} = 3.0 cm^{-3}, sigma_T = 43 K, and sigma_{log(P/k)} = 0.22 cm^{-3} K. Interestingly, the pressures measured in these high redshift CI clouds are similar to those found in the Milky Way. We conclude that the CI gas is tracing a higher-density, higher-pressure region, possibly indicative of post-shock gas or a photodissociation region on the edge of a molecular cloud. We speculate that these clouds may be direct probes of the precursor sites of star formation in normal galaxies at high redshift.

astro-ph.CO↗

arXiv2010

The nature of proximate damped Lyman alpha systems

We present high resolution echelle spectra of 7 proximate damped Lyman alpha (PDLA) systems whose relative velocity separation from the background quasar is Delta V < 3000 km/s. Combining our sample with a further 9 PDLAs from the literature we compare the chemical properties of the proximate systems with a control sample of intervening DLAs. Taken at face value, the sample of 16 PDLAs exhibits a wide range of metallicities, ranging from Z ~ 1/3 Z_sun down to Z ~ 1/1000 Z_sun, including the DLA with the lowest N(SiII)/N(HI) yet reported in the literature. We find several pieces of evidence that indicate enhanced ionization and the presence of a hard ionizing spectrum in PDLAs which lead to properties that contrast with the intervening DLAs, particularly when the N(HI) is low. The abundances of Zn, Si and S in PDLAs with log N(HI) > 21, where ionization corrections are minimized, are systematically higher than the intervening population by a factor of around 3. We also find possible evidence for a higher fraction of NV absorbers amongst the PDLAs, although the statistics are still modest. 6/7 of our echelle sample show high ionization species (SiIV, CIV, OVI or NV) offset by >100 km/s from the main low ion absorption. We analyse fine-structure transitions of CII* and SiII* to constrain the PDLA distance from the QSO. Lower limits range from tens of kpc up to >160 kpc for the most stringent limit. We conclude that (at least some) PDLAs do exhibit different characteristics relative to the intervening population out to 3000 km/s (and possibly beyond). Nonetheless, the PDLAs appear distinct from lower column density associated systems and the inferred QSO-absorber separations mean they are unlikely to be associated with the QSO host. We speculate that the PDLAs preferentially sample more massive galaxies in more highly clustered regions of the high redshift universe.

astro-ph.CO↗

arXiv2009

Lyman break galaxy close and interacting pairs at z ~ 3

To date, the identification of interactions at z ~ 3 and above has relied on morphological analysis. Here, we present five serendipitous spectroscopic z ~ 3 Lyman break galaxy (LBG) pairs with projected proper separations < 15 h^-1 kpc in our survey of nine separate Keck fields. The data consist of 140 of our highest signal-to-noise ratio LBG spectra and ~500 of our most confident colour-selected LBGs. We show that the pairs are composed of two distinct close and/or interacting LBGs from a detailed analysis of the rest-frame ultraviolet spectra and images. In addition, we show that the pair number and separation distribution is expected from (1) the angular correlation function when applied to our survey and ~2500 colour-selected LBGs from the literature and (2) an analysis of a carefully matched high-resolution hybrid numerical and analytical cosmological simulation. Because the spectroscopic slitlets have random orientations with respect to the close pairs on the sky, the serendipitous pairs provide an unbiased sampling of the underlying close pair fraction. Finally, we discover two Ly-a emitters (LAEs) in our slitlets and find that they reside within 50 projected h^-1 kpc of LBGs. In this work, we uncover a strong relationship between Ly-a emission and pair separation. All confirmed and all candidate LBG pairs with separations of < 15 projected h^-1 kpc exhibit Ly-a in emission and we find an overabundance of Ly-a emission in pairs with < 50 projected h^-1 kpc separations. This relationship suggests a picture in which a measurable fraction of the Ly-a emission of LBGs, and potentially LAEs, is generated via interaction mechanisms. As a result, serendipitous spectroscopic close pairs provide a unique means to help identify and study high-redshift galaxy interactions using conventional ground-based optical data.

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arXiv2009

Wavelength Accuracy of the Keck HIRES Spectrograph and Measuring Changes in the Fine Structure Constant

We report on an attempt to accurately wavelength calibrate four nights of data taken with the Keck HIRES spectrograph on QSO PHL957, for the purpose of determining whether the fine structure constant was different in the past. Using new software and techniques, we measured the redshifts of various Ni II, Fe II, Si II, etc. lines in a damped Ly-alpha system at z=2.309. Roughly half the data was taken through the Keck iodine cell which contains thousands of well calibrated iodine lines. Using these iodine exposures to calibrate the normal Th-Ar Keck data pipeline output we found absolute wavelength offsets of 500 m/s to 1000 m/s with drifts of more than 500 m/s over a single night, and drifts of nearly 2000 m/s over several nights. These offsets correspond to an absolute redshift of uncertainty of about Delta z=10^{-5} (Delta lambda= 0.02 Ang), with daily drifts of around Delta z=5x10^{-6} (Delta lambda =0.01 Ang), and multiday drifts of nearly Delta z=2x10^{-5} (0.04 Ang). The causes of the wavelength offsets are not known, but since claimed shifts in the fine structure constant would result in velocity shifts of less than 100 m/s, this level of systematic uncertainty makes may make it difficult to use Keck HIRES data to constrain the change in the fine structure constant. Using our calibrated data, we applied both our own fitting software and standard fitting software to measure (Delta alpha)/alpha, but discovered that we could obtain results ranging from significant detection of either sign, to strong null limits, depending upon which sets of lines and which fitting method was used. We thus speculate that the discrepant results on (Delta alpha)/alpha reported in the literature may be due to random fluctuations coming from under-estimated systematic errors in wavelength calibration and fitting procedure.

astro-ph.CO↗

arXiv2009

Deep Keck u-band imaging of the Hubble Ultra Deep Field: A catalog of z~3 Lyman Break Galaxies

We present a sample of 407 z~3 Lyman break galaxies (LBGs) to a limiting isophotal u-band magnitude of 27.6 mag in the Hubble Ultra Deep Field (UDF). The LBGs are selected using a combination of photometric redshifts and the u-band drop-out technique enabled by the introduction of an extremely deep u-band image obtained with the Keck I telescope and the blue channel of the LRIS spectrometer. The Keck u-band image, totaling 9 hours of integration time, has a one sigma depth of 30.7 mag arcsec^-2, making it one of the most sensitive u-band images ever obtained. The u-band image also substantially improves the accuracy of photometric redshift measurements of ~50% of the z~3 Lyman break galaxies, significantly reducing the traditional degeneracy of colors between z~3 and z~0.2 galaxies. This sample provides the most sensitive, high-resolution multi-filter imaging of reliably identified z~3 LBGs for morphological studies of galaxy formation and evolution and the star formation efficiency of gas at high redshift.

astro-ph.CO↗

arXiv2009

Direct Evidence of Cold Gas in DLA 0812+32B

We present the first direct evidence for cold gas in a high redshift DLA galaxy. We measured several multiplets of weak neutral carbon (CI) transitions in order to perform a curve of growth analysis. A delta chi-squared test constrains the best fit Doppler parameter, b = 0.33_{-0.04}^{+0.05} km/s, and logN(CI) = 13.30 +- 0.2 cm^-2. This Doppler parameter constrains the kinetic temperature of the gas to T <= 78 K (T <= 115 K, 2 sigma). We used the associated CI fine structure lines to constrain the volume density of the gas, n(HI) ~ 40 - 200 cm^-3 (2 sigma), resulting in a lower limit on the cloud size of approximately 0.1 - 1 parsec. While it is difficult to determine the metallicity of the cold component, the absence of Cr II indicates that the cold cloud suffers a high level of dust depletion. Additionally, the large amount of Lyman and Werner-band molecular hydrogen absorption (log N(H2)_{total} = 19.88 cm^-2, f_{H_2} >= 0.06) with an excitation temperature of T_{ex} = 46 K as determined by the rotational J = 0 and J = 1 states, is consistent with the presence of cold gas. We propose that this cloud may be gravitationally confined and may represent a transition gas-phase from primarily neutral atomic gas, to a colder, denser molecular phase that will eventually host star formation.

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